San Francisco Area Forecast Discussion
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 182338 aaa
afdmtr
area forecast discussion
national weather service san francisco ca
430 pm pdt fri may 18 2007
updated aviation
.discussion...satl imagery and sfc obs indc stratus has pretty well
dissipated across the district as well as the coastal waters. with
warmer air moving into the district...the marine inversion has
basically disappeared. temps are generally in the 60s and 70s across
the district. cooler air has made it well inland with the 3.3 mb
onshore flow between sfo-sac. in fact...sacramento is only in the
mid 70s.
satl imagery indc a trof moving to the pacific northwest. this will
keep the onshore flow continuing right through the weekend along
with cool temps. there could be patchy night/morning low clouds as
the marine layer develops again this evening.
temps begin to warm next week as a ridge builds into the west coast.
the warmest days appear to be tuesday through thursday as the flow
is parallel...or slightly offshore. inland temps into the 90s will
be common...with the southern interior sections of monterey county
topping 100. the coast could get a little cooler on thursday as the
thermal trough begins to shift slightly east. inland areas should see
the beginnings of a cool down on friday as the thermal trough shifts
into nevada as the upper ridge begins to break down.
&&
.aviation...vfr conditions prevail over the area this afternoon. the
airmass is slightly warmer and drier. some stratus may develop later
tonight but probably not until well after midnight for sfo...oak and
sjc. mry and sns may see stratus develop between 06z-09z. sts may
see patchy fog briefly sat morning but this should quickly mix out
in the morning.
&&
.mtr watches/warnings/advisories...
.tngt...sca...pigeon point to pt piedras blancas and sfo bay.
&&
public forecast: strobin
aviation/marine: canepa
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Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 190540 cca
afdmtr
area forecast discussion...corrected version
national weather service san francisco ca
1040 pm pdt fri may 18 2007
.discussion...this evenings weather looks quite a bit like 24 hours
ago with the exception that boundary layer humidity a little less
moist. onshore pressure gradient sfo-sac at 3.5mb the same with the
inland gradient sfo-las up about 1mb and ksfo reflecting that strong
onshore push with winds gusting 25kts. max temperatures around the
central california coastal forecast area generally from 1 down to
about 3 up from yesterday although 03z observations showing temps
generally up 2 to 5 degs most areas and up 9 degs at ksts.
do expect stratus to reform late this evening and push onshore again
very late tonight and have adjusted sky cover grids to reflect that
expectation. marine layer beginning to reflect some disruption with
the broad but weak cyclonic flow over northern california. expect
stratus to be more patchy and affecting just monterey and south
s.f.bay early sunday morning. while the main trof axis continues to
be progged through the pac nw early sunday models continue to
maintain relatively unchanging heights over the central coast. have
adjusted temperatures upward slightly for saturday slightly upward
in the grids in the east and east-southeast inland valleys but
essentially have let persistence rule through early sunday. outside
of low cloud areas along the coast fair skies will prevail through
the weekend.
per previous discussion and good model consistency the concern for
the weather from monday through wednesday next week is the mild
offshore wind flow pattern at the surface that will bring about
cleared skies and downslope warming. inland temperatures will rise
with the synoptic warming within the building ridge with coastal
areas having above normal temperatures with no stratus and the
low-level downslope warming. the coast could get a little cooler on
thursday as the thermal trough begins to shift slightly east. inland
areas should see the beginnings of a cool down on friday as the
thermal trough shifts into nevada as the upper ridge begins to break
down.
no change for evening forecast packages with above mentioned tweaks
in grids for next shifts review/refinement/acceptance.
&&
.aviation...a few patches of stratus just developed along the san
mateo coast. the airmass is still slightly warmer and drier compared
to this time last evening. bay area terminals will continue to have
vfr for the next few hours with some stratus possible early saturday
morning just before daybreak. mry and sns may see stratus develop
between 06z-09z. the stratus should mix out fairly quickly saturday
morning.
&&
.mtr watches/warnings/advisories...
.tngt...sca...pigeon point to pt piedras blancas and sfo bay.
&&
public forecast: gudgel
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 191122
afdmtr
area forecast discussion
national weather service san francisco ca
422 am pdt sat may 19 2007
.discussion...satellite imagery shows only patchy stratus has moved
or formed over a few inland areas as of 3 am...but a fairly solid
layer exists over the coastal waters. the marine layer is deep but
diffuse...per the fort ord profiler...with a depth of between 2500
and 3000 feet. surface pressure gradients are moderate onshore with
2.9 mb between san francisco and sacramento...and 11.5 mb from sfo
to las vegas.
a weak but broad upper level trough is currently centered over the
western states. this is forecast to remain in place over the weekend
with little change in temps expected. by monday an upper ridge is
progged to build over the west with an accompanying weak offshore
flow setting up by tuesday. thus...a warming trend is slated to
last through about midweek with clearing skies and downslope
warming. max temperatures are expected to warm into the 60s and 70s
along the coast with 70s and 80s inland...up to the 90s across the
warmest inland areas. medium range models generally keep the upper
ridge over the west through the work week...but a return to onshore
flow after midweek will cool coastal temperatures back to the mid-50
to mid-60 range.
&&
.aviation...onshore flow still prevails and marine layer is rather
diffuse...so morning stratus will be patchy and short lived this
morning. otherwise...winds will breezy once again...esp around sfo
and the bay area. as for tonight...not really expecting a lot of
stratus...mainly confined to the immediate coast.
&&
.mtr watches/warnings/advisories...
.tda...sca...point arena to pt piedras blancas.
&&
public forecast: anderson
aviation/marine: mehle
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 191640
afdmtr
area forecast discussion
national weather service san francisco ca
930 am pdt sat may 19 2007
.discussion...satl imagery indc that stratus is hugging the coast
and is into both monterey and san francisco bays. the marine layer
is at a diffuse 2500 feet this morning...and the airmass above it is
not all that warm...mt diablo raws at 3849 ft is reporting a temp
of 52 degrees. with a trough along the coast the gradient is
northerly from sfo-arcata and onshore between sfo-sac.
with the trough fcst to slowly move onto the coast the onshore
gradient will continue...which will keep the district cool. even
well inland high temps yesterday were only in the 70s...and see no
reason that they would be any different today...considering the
similar pattern.
the current forecast looks good...no updates needed.
&&
.aviation...the stratus is persisting along the coast and continues
to fill in the sfo bay area and approach this morning. the airmass is
slightly warmer and more moist this morning compared to 24 hours ago.
surface dewpoints are up in the upper 40s and lower 50s...similar to
sea surface temps from 48-52f. this is helping to maintain a nearly
widespread stratus field over the waters. had to bump up break out
times to 18z for sfo and oak. mry and sns will also see ceilings
longer than earlier expected with break out times delayed until
18-19z.
after the low clouds clear out later this morning an increasing acv-
sfo pressure gradient will probably help prevent stratus from
reaching back into the bay area later this afternoon and evening.
localized onshore gradients will also increase to 4-5 mb sfo-sac
this afternoon and possibly again sunday afternoon per the wrf
model.
&&
marine...a strengthening sfo-sac gradient this afternoon and again
sunday afternoon may necessitate a small craft advisory for sfo bay
each afternoon/evening. will look into this a bit more and possibly
issue an update to the coastal forecast product soon.
.mtr watches/warnings/advisories...
.tda...sca...point arena to pt piedras blancas.
&&
public forecast: strobin
aviation/marine: canepa
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 192204 aab
afdmtr
area forecast discussion
national weather service san francisco ca
300 pm pdt sat may 19 2007
updated aviation/marine
.discussion...satl imagery indc that stratus is still hugging the
coast and is into both monterey and san francisco bays. the marine
layer has not changed much...still near 2500 feet. and the airmass
above it is not all that warm...mt diablo raws at 3849 ft is
reporting a temp of 55 degrees. however...with a north wind santa
rosa has just warmed to 78 degrees. the gradient picture shows an
increasing north gradient between arcata-sfo...now 4.3 mb compared to
0.8 yesterday and an onshore gradient between sfo-sac of 3.2 mb...
similar to yesterday.
tonight and sunday should be similar to todays weather with little
change in the upper pattern. the trough in the pacific northwest will
slowly move east...with a continued onshore flow.
the upcoming work week will feature a warming trend...especially
inland as a ridge begins to build along the coast and slowly move
inland. high pressure will build into the pacific northwest...which
will turn the flow parallel to the coast. it appears that the thermal
trough will set up slightly inland...which should keep the coast
cool. since 850 mb temps are fcst to warm inland areas should reach
the 90s by the middle of the week. we should see temps top 100 in san
benito and the interior of southern monterey counties. the ridge
begins to break down on saturday as an upper low sags south through
british columbia. this should start to cool down the inland areas as
850 mb temps drop several degrees. basically...typical summer weather
for central california.
&&
.aviation...the stratus has mixed out across the bay area and is now
confined to the immediate coastal sections of san mateo and monterey
counties. a key factor in tonight`s forecast is the strength of the
acv-sfo pressure gradient which continues to ramp up. it`s now 5 mb.
this is on track with the wrf model which puts it at least 5-6 mb
tonight and sunday. sts has been reporting a n-nw wind in the last
few observations which is a response to the increased northerly
gradient. overall am expecting the bay area to remain vfr through the
evening...and most likely all of tonight. some patches of stratus may
stay along the immediate coast affecting mry and sns this afternoon
and again much later tonight. vfr is forecast sunday at area
terminals.
sfo continues to report gusty west winds with occasional gusts to 30
kt. the sfo-sac gradient is currently moderately strong at 3.4 mb and
could climb as high as 5 mb this evening. the depth of the marine
inversion today favors strong winds into the evening at sfo
especially if it ends up combining with a stronger localized gradient
across the peninsula. will hold off on issuing an airport weather
warning for now.
&&
.marine...a stronger northerly gradient over the waters will result
in gusty nw winds. occasional gale force gusts through the evening
and tonight are possible. otherwise small craft advisories are in
effect for the coastal waters as well as sfo bay.
.mtr watches/warnings/advisories...
.tngt...sca...point arena to pt piedras blancas and sfo bay.
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 200532
afdmtr
area forecast discussion
national weather service san francisco ca
1030 pm pdt sat may 19 2007
update aviation/marine
.discussion...skies finally totally cleared for the central coast
forecast area late this afternoon after late arriving and
subsequently persistent stratus in north santa clara valley and
monterey bay area. onshore pressure gradients remaining solid with
3.3mb sfo-sac and sfo-las at 11.7mb...both only down slightly from 24
hrs previous. s.f.airport steady 20kts gusting to 27kts but inland
travis winds lower but steady at 14kts. with the persistent stratus
in many of the southern zones daytime highs were about the same to
lower 4 degrees while north bay areas were the same to up about 3
degrees. east bay inland areas were up 2 to 4 degs.
trof passage into the pacific northwest still on-track for sunday
with post-trof buckling and the onset of the ridge building in the
eastern pacific. a bit of a change in the medium range models short
term with heights actually lowering about 40 meters from sunday to
monday at the h5 level in the northwest flow vs. previous forecast
runs showing little height change before height rises with the aloft
ridge. current forecast package was produced with the previous runs
solution of putting max temperatures for central coast similar to
slightly up from sunday to monday. next forecast package may have to
acknowledge 18z and 00z model runs reflecting some lowering of max
temperatures per synoptic cooling aloft for the monday time period.
no other changes contemplated at this time with high pressure
building aloft from the first to the middle of the coming work week.
locally the weather concern will be the extent of the warming due to
downslope warming tuesday through thursday. interior temperatures
over san benito and southern monterey counties may reach close to
100 degs by wednesday afternoon along with lowered humidities
even for coastal areas. coastal stratus may have difficulty
reforming this evening as profilers reflecting marine layer
disruption and mixing with the aforementioned strong onshore pressure
gradients as well as the strong 6.0mb sfo-acv gradient. the marine
layer disruption tonight with persistent winds and the development of
offshore flow by very late monday for the north coast areas should
remove stratus from the forecasts for the next few days.
&&
.aviation...06z tafs show no ceilings for sunday morning for the
major bay area terminals. for now have hedged with mry and left a
tempo group for the early hours. the strong northerly gradient
seems to have mixed things out nicely and as noted above the
profilers show a disorganized marine inversion.of note will be
strong onshore winds at sfo but they should ease as the northerly
gradient becomes stronger overnight.
&&
.marine...gale warnings have been issued for the southern waters
with several hours of gale force gusts at buoy 28 off the big sur
coast. high end small craft advisories continue over the ocean with
winds easing in the bays at this hour. with current gradient setup
the strongest winds are south of the bay bridge and near sfo. strong
wind and fresh swell to continue sunday.
.mtr watches/warnings/advisories...
.tngt...sca...point arena to pigeon pt and sfo and mtr bays
gale warning...pigeon pt to pt piedras blancas.
&&
public forecast: gudgel
aviation/marine: r walbrun
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 201126
afdmtr
area forecast discussion
national weather service san francisco ca
426 am pdt sun may 20 2007
.discussion...surface observations across the district reveal mostly
clear skies...or at least a lack of fog...at area airports. satellite
imagery shows a swath of high clouds over the northern half of the
state which is obscuring the view of what is occurring beneath. these
high clouds are associated with an upper level trough now moving into
the pacific northwest. onshore surface pressure gradients remain
fairly strong with over 3 mb between sfo and sac...and 11 mb from
sfo to las vegas. in addition...the arcata to san francisco gradient
is pushing 5 mb. the fort ord profiler does not show a strong
marine inversion...thus only expect patchy fog to develop right at
the immediate coast if at all this morning.
the upper trough is progged to move eastward into the great basin
on monday with strong high pressure building over the eastern
pacific. this ridge will begin edging towards the west coast early in
the week for a dramatic warming trend. in addition...an offshore
flow is forecast to briefly develop monday night with some gusty
winds possible in the north and east bay hills by tuesday morning.
warm temperatures to continue through the work week as the upper
trough slowly moves overhead. the trough is progged to weaken by
next weekend...but even though medium range progs bring an upper
trough towards the coast by next weekend...conditions to remain
benign for the upcoming holiday weekend...albeit cooler at the coast
in a renewed onshore flow.
&&
.aviation...profilers this am do show a weak marine layer near 2k ft
and gradients are still onshore...but the n-s gradient is stronger
than the onshore gradient. stratus may be poss this am...but not
forecasting it for bay area terminals as n-s gradient is 4-6mb.
however...mry bay area may still have a shot and will cont with
tempo group. otherwise...high clouds will prevail with gusty winds
once again. the onshore gradient is forecast to weaken later today
so winds should diminish late this evening.
&&
.marine...no real changes with marine hazards. gale force winds are
still being reported at buoy 28 as of 4am. elsewhere...sca winds
are being met with the exception of the bays. the onshore gradient
is forecast to remain strong through this evening so winds across
the bays should increase this afternoon.
.mtr watches/warnings/advisories...
.tda...sca...point arena to pigeon pt and sfo and mry bays
gale warning...pigeon pt to pt piedras blancas.
&&
public forecast: anderson
aviation/marine: mehle
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 201806
afdmtr
area forecast discussion
national weather service san francisco ca
1100 am pdt sun may 20 2007
updated for local stratus into bay area tonight...
see aviation discussion
.discussion...sfc obs indc mainly clear skies across the district
this morning with temps in the 40s and 50s. just a few high clouds
are moving across the district...the southern extent of a trough in
the pacific nw. the marine layer is near 2200 feet this morning...
and pretty diffuse...the probable reason that there is little
stratus. the gradient picture is similar to yesterday...with the
northerly gradient between arcata-sfo at 3.3 mb...compared to 3.5 mb
yesterday. the sfo-sac gradient is onshore at 2.5 mb...same as
yesterday.
the upper trough is fcst to move inland into the pacific northwest
today and tonight. this will keep the flow onshore...with cool temps
at the coast and near normal temps inland. ridging builds in for a
warm-up next week.
fcst looks good...no updates.
&&
.updated aviation...while marine layer still expected to be diffuse
tonight boundary layer moisture progs strongly rebuilding moisture
field along the coast. have adjusted 18z tafs for s.f.bay and
monterey to reflect local intrusion of stratus over terminals late
this evening. feel that marine layer weakened enough to perhaps keep
bridge approach open to ksfo despite broken deck over the airfield
after 06z. inland intrusion anticipated to be minimal with the
diffuse marine layer despite onshore flow. moderate to strong onshore
winds diminishing by late evening to light onshore.
&&
.marine...with moderate n-s pressure gradients still in place along
with afternoon enhancement will maintain sca for northern waters and
s.f.bay into mid-evening hours with gale warning remaining through
same time period for south waters. lowered sca for monterey bay with
sheltering providing winds in the 15 to 20 kt range.
.mtr watches/warnings/advisories...
.tda...sca...point arena to pigeon pt and sfo bay
gale warning...pigeon pt to pt piedras blancas.
&&
public forecast: strobin
aviation/marine: gudgel
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 202253 aaa
afdmtr
area forecast discussion
national weather service san francisco ca
400 pm pdt sun may 20 2007
updated aviation
.discussion...satl imagery indc clear skies along the central ca
coast this aftn. a cold front is moving into northwest ca. latest ft
ord profiler indc a weak inversion. temps are running a few degrees
warmer this aftn compared to yesterday...mainly in the 60s and 70s...
with santa rosa reporting 81 degrees. in san benito and the interior
of monterey county temps are in the 70s to upper 80s. the northerly
gradient between arcata-sfo has relaxed to 2.5 mb...compared to 4.8
mb yesterday. the onshore sfo-sac gradient is a robust 3.9 mb...
compared to 3.3 mb yesterday. with the increased onshore gradient
and weaker northerly gradient winds have picked up in the san
francisco bay area...with sfo reporting a west wind sustained at 35
kt gusting to 42 kt.
as the trough in the pacific northwest moves inland and deepens
tonight and monday...with ridging building into the coast by the
middle of the week. as the trough deepens monday night...the
pressure gradient steepens...with the winds looking like they will
be quite gusty. as the ridge continues to build along 130 w...the
flow aloft will be north to northwesterly. this will allow the
coast to keep cool...with localized sea breezes every aftn as the
thermal trough remains east of the coast. inland areas will heat
up...with 90s common by the middle of the week. in the southern
interior of monterey and san benito counties temps could top 100.
another shortwave dives into the pacific northwest/northern
intermountain west for a return of onshore flow and slightly cooler
temps by the end of the week.
basically...typical late spring weather is in store for the district
for the upcoming week.
&&
.aviation...locally gusty onshore winds this afternoon. sfo will
have strong gusty west winds through 04z. sfo-sac is 3.9 mb.
&&
.mtr watches/warnings/advisories...
.tngt...sca...point arena to pigeon pt and sfo bay.
gale warning...pigeon pt to pt piedras blancas.
&&
public forecast: strobin
aviation/marine: canepa
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 210513 aaa
afdmtr
area forecast discussion
national weather service san francisco ca
1015 pm pdt sun may 20 2007
updated aviation
.discussion...very strong winds this evening near sfo with several
hours of gusts in excess of 35 knots which prompted the issuance of
an airport weather warning. spotter in the city reported 35 mph
earlier and a nowcast was issued for coast and bayside locations.
winds are slowly easing in most areas and this trend will continue
overnight. just a few hours ago the coast was clear with nothing
but clear skies over the ocean. over the the last couple of hours a
large stratus field has quickly developed and has begun to spread
onto the coast with ceilings already being reported at sfo...mry
and sns. therefore zones and grids were updated to increase cloud
cover overnight.
the synoptic lift responsible for the rapid cloud formation is in
association with a shortwave moving into the pacific northwest. as
this system moves into the great basin on monday another strong
northerly/down coast gradient will develop. this is once again
expected to quickly mix out most of the clouds both along the coast
and over inland areas. model cross sections indicate rapid drying
of the lowest levels of the troposphere after 15z monday. overall
the airmass temperature stays about neutral although by tomorrow
afternoon the onshore flow should be much weaker than today and be
more northerly. all in all expect readings similar or slightly
warmer on monday.
fairly noteworthy transition occurs monday night into tuesday as a
quick but potentially significant offshore wind event sets up for
portions of our cwa and much of the central valley. once again the
models indicate rapid drying will occur by later tomorrow afternoon
and night with moderate to strong north winds developing especially
over napa county and portions of the north and east bay hills. main
concern here will be fire weather. models indicate little or no rh
recovery in the hills with sustained north to northeast winds
easily in the 15-30 mph range with frequent gusts to 40 mph appearing
likely. if we were later in the summer this would be a definite red
flag event. however the fly in the ointment right now is that the
fuels are still greening up. but we all know that things are much
drier than normal for may. for now have strongly worded the fire
weather forecast and will coordinate conference calls on monday
with land management agencies. either way the event will not be long
lasting with winds turning onshore again by wednesday after a warm
and dry day on tuesday for nearly the entire cwa...especially inland.
the 00z gfs keeps a baggy trough over our region for the second half
of the work week with onshore winds and seasonable temps while the
12z ecmwf keeps the trough further east with more ridging over our
region. either way no rain or other significant changes of note in
site for the extended.
&&
.aviation...the airmass continues to produce stratus in a low level
stable environment. sfo...mry and sns report ceilings now. basically
looking for the stratus to continue moving inland on onshore breezes
overnight. the stratus will probably not break out until late morning
monday at the earliest.
&&
.mtr watches/warnings/advisories...
.tngt...sca...point arena to pigeon pt.
&&
public forecast: r walbrun
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 210947
afdmtr
area forecast discussion
national weather service san francisco ca
240 am pdt mon may 21 2007
.discussion...an upper level trough...currently located over the
pacific northwest and responsible for a nocturnal lightning event
over central and eastern oregon...will move southeast into the great
basin as an upper ridge builds over the eastern pacific. these
features will set the stage for a pattern shift across the bay area
this afternoon through most of wednesday which will feature above
normal temperatures and dry offshore winds resulting in fire
weather concerns.
we are still dealing with the last of the marine layer this morning
from the golden gate south into the santa clara and salinas
valleys. the profiler data at fort ord shows this inversion layer is
very shallow...approximately 500-800 feet. this also confirmed with
asos obs showing low stratus ceilings and there is sure to be patchy
fog to be dealt with in foothill locations. these conditions should
rapidly clear during the rest of the morning hours as the flow
turns sharply north and strong subsidence takes over. this subsident
airmass will feature much lower moisture content which along with
downsloping offshore flow will result in much warmer temperatures
in many inland locations. lesser warming is expected today along the
immediate coast as flow will bend and eddy onshore in those
locations. have boosted forecast maxes today...and tuesday and
wednesday for that matter...well above mos values in anticipation of
this developing offshore pattern. breezy conditions are expected
this afternoon in areas favored by northerly oriented gradient
pattern such as the north and east bay hills and along the exposed
coastal headlands. tuesday looks to be the warmest day along the
coast although wednesday will probably be very close as onshore flow
may be slow to develop wednesday afternoon. inland areas will
probably be slightly warmer wednesday than tuesday.
it is pretty early in the year to be hoisting fire weather
highlights...but drier than normal fuels and the combination of low
daytime humidities...poor nighttime recoveries and locally breezy
conditions could result in some fire weather issues and this will
be noted in the morning fire weather forecast product.
models are in disagreement over the upper level pattern evolution
late this week with the gfs more troughy along the west coast and an
offshore ridge and the ec positioning the upper ridge closer to the
coast. both models offer similar resulting sensible weather for the
bay area with a weak onshore flow and coastal marine layer with
temperatures near normal. have left the extended forecast period
largely unchanged.
&&
.aviation...previous discussion...the airmass continues to produce
stratus in a low level stable environment. sfo...mry and sns report
ceilings now. basically looking for the stratus to continue moving
inland on onshore breezes overnight. the stratus will probably not
break out until late morning monday at the earliest.
&&
.mtr watches/warnings/advisories...
.tda...sca...point arena to pigeon pt.
&&
public forecast: brenchley
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 211625
afdmtr
area forecast discussion
national weather service san francisco ca
925 am pdt mon may 21 2007
.discussion...stratus is prevalent per satl imagery mainly south of
the golden gate this morning. in fact...early this morning stratus
was down the entire salinas valley to paso robles...while the north
bay was essentially clear. the decrease in stratus in the north bay
is due to the increasing northerly gradient from arcata to sfo...up
to 6.4 mb compared to 3.3 mb yesterday morning. with the onshore
gradient from sfo-sac down to 1.9 mb compared to 2.5 mb yesterday
morning...downslope conditions are occurring in the north bay.
as the upper trough in the pacific northwest moves east high pressure
will build into washington and oregon. this will turn the flow to the
northeast...continuing the drying process...and with downslope
conditions the north bay could be in for some very warm temps.
will not be updating the forecast...looks to be on track for today.
however...the 06z gfs...and a glance at the 12z gfs are both indc
significant changes for later this week...as well as next week...
with cooler conditions. will wait til the 12z euro before jumping on
the gfs changes.
&&
.aviation...overnight stratus clearing along the coast with residual
stratus monterey and nw salinas valley likely cleared by 1730z.
stratus tops around 17 hundred feet msl. n-s pressure gradient strong
with 6mb acv-sfo and moderate onshore gradients. do not expect
stratus to push inland tonight with such gradients so terminals for
the day and tonight to reflect cleared skies. problem of the day for
aviation is locally gusty west wind vicinity of ksfo to 30kts
expected. local gusts yesterday reached 42kts at ksfo prompting local
warning and will watch closely today for similar need.
&&
.marine...models remaining consistent in easily maintaining
northwest wind flow 15 to 25 kts as high pressure in the eastern
pacific builds to midweek. high-end sca extended to tuesday evening
and will need to monitor for possible gale warning northern coastal
waters.
&&
.mtr watches/warnings/advisories...
.tda...sca...point arena to point piedras blancas.
&&
public forecast: strobin
aviation/marine: gudgel
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 212256 aaa
afdmtr
area forecast discussion
national weather service san francisco ca
400 pm pdt mon may 21 2007
updated aviation
.discussion...stratus has cleared the coast this aftn in the strong
northerly flow. temps are in the 60s along the coast to the 80s
inland this aftn. with the northerly flow...and warmer temps aloft...
temps are warmer across the inland areas. the northerly gradient has
really ramped up this aftn between arcata-sfo...now 7.7 mb compared
to 2.5 mb yesterday. the onshore gradient between sfo-sac is 2.3
mb...compared to 3.9 mb yesterday.
models are in disagreement concerning the pattern the end of the
week...as well as the weekend. the gfs is dropping an upper low out
of northwest alberta into northern montana by friday morning. the
euro keeps more of a flat flow across the pacific. the bottom line
will be that temps will not warm up as much as previously thought...
more towards seasonable levels.
next week models continue in disagreement with the gfs fcsting a
sharp trough along the coast while the low res euro keeps a much
broader trough. either way...temps will remain near normal with
continued dry weather.
&&
.aviation...a dry northerly flow will prevail through the night and
tuesday. the acv-sfo gradient is up to 8 mb. forecast is vfr through
the period.
&&
.marine...a strong northerly gradient will cause gusty n-nw winds
over the waters tonight.
&&
.mtr watches/warnings/advisories...
.tngt...sca...point arena to point piedras blancas
sca...rough bar conditions.
&&
public forecast: strobin
aviation/marine: canepa
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 220343
afdmtr
area forecast discussion
national weather service san francisco ca
830 pm pdt mon may 21 2007
.discussion...the acv-sfo gradient is now 9 mb. the wrf model shows
the acv-sfo gradient will be at least 6 mb tuesday and tuesday night.
a northerly flow has introduced a drier weather regime leading to
clear skies district-wide. the warmest places often end up being the
recipients of maximum downsloping effects such as santa rosa where it
was 82f today. all in all dry and clear weather is forecast tue...wed
and thu. some coastal clouds will likely return fri and over the
holiday weekend but temperatures should be near seasonable
everywhere.
&&
.aviation...vfr through tuesday at area terminals.
&&
.marine...gale force gusts have been observed over the northern
waters this evening. sustained winds are slowly climbing to low end
gale warning criteria so will upgrade the northern waters to a gale
warning tonight. small craft advisories continue over the southern
waters with localized gale force gusts a possibility.
&&
.mtr watches/warnings/advisories...
.tngt...gale warning...point arena to pigeon point
sca...pigeon pt to piedras blancas
rough bar conditions.
&&
public forecast: canepa
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 221036
afdmtr
area forecast discussion
national weather service san francisco ca
330 am pdt tue may 22 2007
.discussion...clear skies over the cwa as the central california
coast sits under the right side of a high amplitude upper level
ridge. the axis of this ridge now lies between longitudes 130w and
140w and will weaken tuesday night. by wednesday night...a trough to
the west of the ridge will dig south and pump up the ridge again.
500 mb heights will oscillate slightly in this pattern but not to
the point of causing significant changes in short-term weather.
at the surface a thermal trough over central california is
maintaining offshore flow which has removed the cool moist marine
layer with warm...dry downslope winds. maximum temperatures
tomorrow should be warmer by 5-10 degrees. the coast will enjoy temps
in the 70`s while inland spots warm up to the mid 80`s and lower
90`s. offshore flow continues into wednesday causing little change
in temps but then weakens as onshore flow sets in during the day on
thursday. the gfs model also shows a shortwave sliding down the upper
level ridge thursday afternoon while the ecmwf model does not lower
h5 heights. regardless of model agreement on the upper level
pattern...there will likely be a return of stratus by friday morning
as the marine layer develops along the coast by thursday night with
the onshore flow.
the return of the marine layer will gradually lower temperatures
over the memorial day weekend and the airmass aloft will also cool a
few degrees by sunday. however...temps should only drop a few
degrees below normal and low clouds on the coast and in coastal
valleys should burn off by afternoon.
&&
.aviation...vfr through tuesday at area terminals.
&&
.mtr watches/warnings/advisories...
.tdy...sca...point arena to point piedras blancas.
&&
public forecast: bingaman
aviation/marine: canepa/brenchley
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 221719
afdmtr
area forecast discussion
national weather service san francisco ca
1019 am pdt tue may 22 2007
.discussion...another beautifully clear day across the region greets
us this morning. the only clouds in the sky exist in the monterey
bay and are expected to remain primarily off the coast.
surface high pressure will persist over the eastern pacific with a
thermal trough situated over the state. aloft the central coast is in
between a ridge of high pressure to the west and a trough of low
pressure to the east. little change is expected in the pattern aloft
however at the surface the thermal trough will strengthen and shift
slightly offshore resulting in a stronger offshore pattern.
the current slightly offshore flow is maintaining dry and warm
conditions across the region. temperatures will climb today anywhere
from 5 to 10 degrees over yesterday highs with coastal regions
experiencing temperatures in the 70s while the warmest inland
locations soar to the lower 90s. expect much of the same on wednesday
as the pattern holds steady. by thursday the thermal trough weakens
and the onshore flow resumes once again. models are in a slight
disagreement as to the solution on thursday. the gfs has a shortwave
digging down over the central coast while the euro shows little
change. nonetheless with the return of the onshore flow bringing
increasing moisture to the coast we will see a return of the stratus
overnight on thursday night. by friday and on into the weekend
temperatures will begin to cool especially at the coast with the
return of the marine layer.
present forecast looks good no updates expected.
&&
.aviation...vfr through tonight at all area terminals. only concern
will be poss llws at koak as more ne winds dev in the hills.
&&
.mtr watches/warnings/advisories...
.tdy...sca...point arena to point piedras blancas.
&&
public forecast: c walbrun
aviation/marine: mehle
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 230021
afdmtr
area forecast discussion
national weather service san francisco ca
520 pm pdt tue may 22 2007
updated aviation
.discussion...skies across the central coast remain clear this
afternoon with hotter and drier conditions being felt throughout.
as anticipated temperatures are running up to 10 degrees warmer than
yesterday across the board.
high pressure continue to dominate the weather picture across the
eastern pacific with a thermal trough situated over the california
interior. aloft we are situated between a ridge of high pressure
over the eastern pacific and a trough of low pressure over the great
basin.
latest model runs show very little change from the previous run.
therefore little change will be seen in the afternoon forecast
package. the pattern aloft shows little change or impact over our
area of concern through the end of the work week. at the surface
however at the surface the thermal trough is anticipated to
deepen and shift to the coast resulting in a more pronounced
offshore pattern. the offshore flow will maintain dry and warm
conditions across the region on wednesday as the pattern holds
steady. by thursday the thermal trough weakens and the onshore flow
resumes once again. models have not come to a consensus as to the
solution on thursday. the gfs has a shortwave (although weaker
than in the previous 06z run) digging down over the central coast
while the euro shows little change in the 500 mb height field.
nonetheless with the return of the onshore flow bringing increasing
moisture to the coast we will see a return of the stratus overnight
on thursday night. by friday and on into the weekend temperatures
will begin to cool especially at the coast with the return of the
marine layer.
&&
.aviation...vfr through tonight at all area terminals. only concern
will be poss llws at koak as more ne winds dev in the hills. gusty
winds at ksfo...currently 25 kt...will drop to 12 kt at 04z and to
5 kt by 07z. gusty winds at koak and ksjc will drop below 10 kt by
05z.
&&
.mtr watches/warnings/advisories...
.tngt...sca...point arena to point piedras blancas.
&&
public forecast: c walbrun
aviation/marine: mehle/strobin
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 230417
afdmtr
area forecast discussion
national weather service san francisco ca
917 pm pdt tue may 22 2007
.discussion...under sunny skies today...temperatures were overall
warmer than yesterday`s with highs ranging from the lower 60s at
the coast to the 70s and 80s inland. the warmest reaches of southern
monterey and san benito counties did warm into the lower 90s...but
just barely. the temperature trends ranged from 2 to 10 degrees
warmer than highs on monday.
high pressure continues over the eastern pacific with strong
northwest flow across the coastal waters. a moderate to strong
northerly surface pressure gradient exists with 7.6 mb between
arcata and san francisco and 6.3 mb from winnemucca to sfo.
northerly winds are still occurring over the north and east bay
hills with mount diablo picking up gusts to 32 mph. these northerly
or northeasterly breezes are expected to persist overnight...but
will diminish on wednesday as the wind flow becomes more onshore.
by thursday the upper ridge is forecast to begin weakening over
the eastern pacific with onshore flow ramping up across the district
through the rest of the week and into the weekend. thus...a gradual
cooling trend is indicated to begin on thursday...and continue
through the weekend with temperatures leveling off by early next
week. no forecast updates anticipated.
&&
.aviation...previous discussion...vfr through tonight at all area
terminals. only concern will be poss llws at koak as more ne winds
dev in the hills. gusty winds at ksfo...currently 25 kt...will drop
to 12 kt at 04z and to 5 kt by 07z. gusty winds at koak and ksjc will
drop below 10 kt by 05z.
&&
.mtr watches/warnings/advisories...
.tngt...sca...point arena to point piedras blancas.
&&
public forecast: anderson
aviation/marine: strobin
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 231022
afdmtr
area forecast discussion
national weather service san francisco ca
315 am pdt wed may 23 2007
.discussion...offshore flow will continue this morning though it will
weaken during the day and transition to onshore flow by evening. the
offshore downsloping winds in the first part of the day will warm the
airmass though max temps today will likely be similar or only 2 to 5
degrees warmer than tuesday.
upper level weather pattern...central california remains on the right
side of a ridge that will flatten on friday as a trough in the gulf
of alaska moves towards canada. a series of shortwaves will pass to
the north of california over the weekend ahead of the deepening
trough.
surface weather pattern...on wednesday...both the gfs and nam models
indicate that the thermal trough will retreat inland which will open
the door for the marine layer to develop with onshore flow. as the
marine environment influences the region...max temps will start on a
downward trend beginning thursday through sunday and coastal stratus
will return. once temps have cooled down they should remain fairly
consistent monday through wednesday with coastal max temps in the mid
50s to mid 60s while inland max temps range from the low 70s to low
80s.
&&
.aviation...vfr through tonight at all area terminals.
&&
.mtr watches/warnings/advisories...
.tdy...sca for hazardous seas...point arena to point piedras
blancas.
&&
public forecast: bingaman
aviation/marine: brenchley
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 231524
afdmtr
area forecast discussion
national weather service san francisco ca
824 am pdt wed may 23 2007
.discussion...rather quiet start to the day as only mid-high level
clouds are passing over the cwa.
temperatures are starting off a few warmer than yesterday thanks to
the continued offshore flow. in fact...there are a few places that
are experiencing extraordinary warming compared to yesterday at this
time. for example...san francisco downtown and san rafael are both
16 degrees warmer with most other locations 3 to 8 degrees warmer.
along with the offshore flow...a weak southerly surge is also noted
with higher pressures recorded south of big sur. this can also be
seen on the vis satellite as an area of stratus is moving northward
just off the big sur coast.
the new short range guidance shows the offshore flow weakening
through the day and eventually becoming onshore by tonight. the new
onshore flow will allow for an increase in boundary layer moisture
and put an end to the nice warm weather. max temps will not drop
dramatically over the next few days...but some cooling will be
noticed. a return of the morning stratus and fog will also be felt
across the coastal region through the rest of the week.
&&
.aviation...vfr through tonight at all area terminals.
&&
.mtr watches/warnings/advisories...none
&&
public forecast: mehle
aviation/marine: soroka
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 240003
afdmtr
area forecast discussion
national weather service san francisco ca
455 pm pdt wed may 23 2007
updated aviation
.discussion...challenges with this forecast include cooling trend
into the weekend and return of stratus.
ample sunshine and continued offshore flow have allowed for great
warming across the cwa this afternoon. in fact...most locations are
4 to 8 warmer with a few locations around sf bay 10 to
15 warmer than yesterday. the other item of note this afternoon is
the southerly surge along the big sur coast. ample low clouds
streamed northward along the coast...which started this morning. a
quick look at the goleta profile has the marine layer near 3500ft
while the ft ord profiler has the very diffuse marine layer near
1000ft. in other words...the stratus is rolling downhill from south
to north.
otherwise...only minor tweaks were made to the forecast. guidance
is in decent agreement with the weakening of offshore flow and
increased onshore flow. this will start to take shape this evening...
which will temper the strong winds in the east bay hills seen this
morning. as onshore flow increase...boundary layer moisture will
also increase and temperatures will gradually decrease into the
weekend. the coastal region will see the biggest change over the
next few days with cooler temps and more stratus/fog. by friday
night/saturday morning a weak shortwave trough will traverse the
region and have introduced patchy drizzle for the coast. the overall
forecast looks to remain dry through the forecast period as well.
&&
.aviation...a weak southerly surge brought some coastal low clouds
as far north as half moon bay before stalling there. given the
shallow depth at its northern end and the absence of any indication
it will progress farther northward overnight...expect vfr
conditions to continue at sfo bay area airports tonight through
thursday. with stratus already beginning to work its way from
monterey bay into the northern salinas valley however...do expect
ceilings to develop at ksns during the evening and at kmry by about
midnight along with some reduction in visibilities. clearing at
these terminals is expected by mid-morning tomorrow.
&&
.mtr watches/warnings/advisories...none
&&
public forecast: mehle/anderson
aviation/marine: blier
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 240514
afdmtr
area forecast discussion
national weather service san francisco ca
1012 pm pdt wed may 23 2007
updated aviation and advisories
.discussion...although a southerly surge of stratus was making its
way up the coast today...enough sunshine gave warmer temperatures to
most locations in the district. even a sunny downtown san francisco
warmed to 82 degrees today...up 14 degrees over tuesday`s max temp.
the exceptions to the warming rule were places like santa cruz and
watsonville...along south-facing beaches subject to the cooling
effects of the shallow marine layer that worked its way up the coast
to about half moon bay by mid afternoon. highs today ranged from the
60s and lower 70s at the beaches to the 80s and 90s inland. santa
cruz and watsonville airport both topped out at 63 degrees compared
to 73 degrees at the monterey airport.
satellite imagery currently shows a patchy stratus layer along the
central coast and also confined within the monterey bay. there are
also high clouds filtering over the western states from the north.
surface pressure gradients indicate a moderate northerly gradient
persists between arcata and san francisco with 4.9 mb between those
sites as of last hour. in addition...a 2.0 mb gradient exists
between sfo and sac...while a weak southerly gradient shows up with
1.4 mb from santa maria to san francisco. the fort ord profiler
indicates an inversion layer at a depth of around 1000 feet.
given the shallowness of this layer as well as the patchiness of the
stratus off the coast...believe only local intrusion of the low
clouds tonight. have issued a forecast update to warm many max
temperatures across the district for thursday...and to indicate
less cooling on friday. this is substantiated by latest model
guidance keeping the upper ridge over the eastern pacific and
holding off a strong onshore push until closer to the weekend when
the upper ridge weakens and gives way to a zonal flow aloft across
the west coast and a tightening of the onshore surface pressure
gradients. this will result in an increasing marine layer and a
marked cooling trend heading into the holiday weekend.
&&
.aviation...a weak southerly surge brought some coastal low clouds as
far north as half moon bay earlier today...before stalling and
then eroding from the north. vfr conditions are expected to continue
at sfo bay area airports overnight through thursday. close call
as to whether residual area of stratus remaining in the vicinity of
monterey bay will manage to work its way southward over kmry and
ksns. given slow but steady shift in that direction evident in fog
product satellite imagery over past couple of hours...will go with
ceilings developing overnight at these 2 terminals.
&&
.mtr watches/warnings/advisories
tngt...sca pt arena to pt reyes until 3 am
...sca sfo bay n of bay bridge until 3 am
&&
public forecast: anderson
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 241145
afdmtr
area forecast discussion
national weather service san francisco ca
450 am pdt thu may 24 2007
updated aviation discussion
.discussion...current satellite fog product shows a wedge of stratus
in the southern coastal waters. movement of the coastal stratus is
similar to the southerly surge from yesterday as the tip of this
wedge is moving northward along the immediate coastline...just past
pigeon point towards half moon bay. the fog has also enveloped
monterey bay and is quickly filling the salinas valley.
part of the reason for this southerly surge is due to a much weaker
north-south gradient...only 3 mb from arcata-sfo compared to the 7
mb difference 24 hours ago. this surge will once again affect max
temperatures for the vulnerable santa cruz and watsonville as they
face the oncoming cool flow of the marine layer...highs for these
spots and other places along the immediate coast will likely only
reach the mid 60s. inland locations should heat up into the mid 70s
to mid 80s since the onshore gradient is only at 1.4 mb which won`t
provide much of an inland push for the cooling stratus.
as the marine layer begins to re-establish itself...max temperatures
region-wide will be on a downward trend through the weekend. the nam
model shows the onshore gradient increasing to almost 4 mb starting
friday afternoon. thus...the holiday weekend will have slightly
below normal temps with areas of night and morning fog affecting
the coast and coastal valleys.
between monday and wednesday...temps should warm a few degrees as the
upper level pattern transitions from nearly zonal over the weekend to
ridging. a storm in the gulf of alaska will be moving towards the
west coast pushing a ridge ahead of it during the first part of the
week.
&&
.aviation...vfr conditions expected at san francisco bay area
terminals today. shallow marine layer fog and stratus continues to
affect the monterey bay terminals with ifr/lifr conditions. fog
product satellite shows this stratus/fog has crept up the pacific
coast from half moon bay to southern marin county in the past hour.
however with very weak onshore flow...do not expect this cloud layer
will move much past the golden gate bridge-angel island area this
morning. the marine layer is expected to make a stronger inland push
tonight bringing low ceilings over the oak terminal and in the
vicinity of sfo.
&&
.mtr watches/warnings/advisories
tdy...none
&&
public forecast: bingaman
aviation/marine: brenchley
nws on the web at weather.gov/sanfrancisco
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 241753
afdmtr
area forecast discussion
national weather service san francisco ca
1055 am pdt thu may 24 2007
.discussion...weak onshore flow has definitely returned this
morning with area pressure gradients at 1-2mb (sfo-sac). the
southerly surge of stratus off the big sur coast from yesterday
continued overnight and actually pushed a little further north this
morning. the first few images of the morning vis satellite shows
widespread stratus stretching from the big sur coast through
monterey bay and sneaking up the san mateo coast toward point reyes.
the inland intrusion is minimal thanks to weak onshore flow and a
marine layer that is only 1000ft thick.
an item of bigger note...are the much cooler temperatures this
morning. the airmass has cooled dramatically with almost all
locations cooler at 8am today compared to yesterday. in fact...a
few locations around the n bay and sf bay are 10-15 degrees cooler.
despite a cool start this morning...temperatures should rebound
nicely under ample sunshine. however...coastal locations will not
rebound as much and should come in cooler today than yesterday.
not expecting much change with the extended forecast through the
holiday weekend. dry conditions with a slight cooling trend will
be felt across the cwa. no updates at this time.
previous extended...
as the marine layer begins to re-establish itself...max temperatures
region-wide will be on a downward trend through the weekend. the nam
model shows the onshore gradient increasing to almost 4 mb starting
friday afternoon. thus...the holiday weekend will have slightly
below normal temps with areas of night and morning fog affecting
the coast and coastal valleys.
between monday and wednesday...temps should warm a few degrees as the
upper level pattern transitions from nearly zonal over the weekend to
ridging. a storm in the gulf of alaska will be moving towards the
west coast pushing a ridge ahead of it during the first part of the
week.
&&
.previous aviation...vfr conditions expected at all area terminals
today. stratus along the coast will persist through the forecast
period with an early onset anticipated at kmry and ksns this evening.
ksfo and koak will also be affected later tonight as the marine layer
moves locally inland.
&&
.mtr watches/warnings/advisories
tdy...none
&&
public forecast: mehle
aviation/marine: c walbrun
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 250005
afdmtr
area forecast discussion
national weather service san francisco ca
504 pm pdt thu may 24 2007
.discussion...challenge with this forecast will be extent of
stratus and fog as the marine layer becomes re-established.
not much has changed since this morning regarding the surface
pattern. inland locations are finally rebounding from the cool start
they experienced this morning. most inland locations will see highs
this afternoon in the 70s and 80s. meanwhile...the coast remains cool
thanks to lingering stratus and increased onshore flow.
the main weather feature that will dominate into the holiday weekend
will be increased coastal stratus and patchy fog with a slight cool
down. upper high level pressure will remain over the epac through
early friday before going zonal. this will keep the cwa under
northwest flow through sunday. sunday into monday...a weak shortwave
trough will traverse the region. this shortwave may cause a brief
disruption in the marine layer...but any dissipated stratus will
quickly return tuesday. generally speaking...temperatures will cool
through saturday and then moderate into next week. still no precip in
the foreseeable future.
&&
.aviation...low clouds are starting to amass along the coast but the
marine layer depth remains fairly shallow...around 1000 feet deep
per the fort ord profiler data. the surface pressure gradients
continue to be moderate-to-strong northerly with 3.0 mb between acv
and sfo...and 4.8 from sfo-las. 2.3 mb between sfo and sac last
hour indicates an increasing onshore flow. expect an early ceiling
at monterey and salinas airports tonight...around 03z or 04z.
ceiling formation will be later at bay area airports given the
northerly flow...after midnight local time.
&&
.mtr watches/warnings/advisories
tngt...none
&&
public forecast: mehle
aviation/marine: anderson
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 250343
afdmtr
area forecast discussion
national weather service san francisco ca
848 pm pdt thu may 24 2007
.discussion...cooler day in most areas today as onshore flow has
strengthened and marine layer begins to deepen. southerly surge
that began yesterday around monterey bay actually weakened
somewhat...yielding warmer temperatures for santa cruz and
watsonville. in addition...almost all locations in interior monterey
and san benito county were warmer today as airmass aloft warmed
overhead. however...the heart of the bay area experienced general
drops from 3 to 8 degrees...with the biggest losers san francisco
downtown (18 degrees cooler)...pacifica (14 degrees lower) and
south san francisco (19 degrees cooler). northerly gradient down
the coast remains around 4mb sfo/acv and nearly flat from sfo/sba.
ft.ord profiler confirms marine layer depth up to around 1500ft
with more robust onshore winds than 24hrs ago. last visible imagery
earlier this evening showed a thicker stratus layer developing along
the coast penetrating through the golden gate and along
the san mateo...santa cruz and monterey lines and locally inland.
bigger picture per water vapor imagery shows upper ridge flattening
off the pac nw coast as various short-waves spit out of upper low
spinning near 53n/160w.
short-range models point to another push of near-shore south flow
around monterey bay fri morning as thermal low pressure ejects
inland. this will serve to continue the deepening of the marine
layer allowing low clouds to push a bit further inland tonight.
dont expect clouds however to reach across into east bay or south
bay valleys just yet. only subtle changes in upper heights thru
fri...but continued rather warm temperatures aloft and stronger
onshore push will firm up inversion and keep coastal
temperatures cool and drop inland highs a bit by afternoon. much more
significant stratus intrusion expected fri night as thermal low
pushes toward the valley and opens up offshore air conditioning.
waves aloft will also deepen marine layer up to 2000ft or higher by
saturday. this will make for an overcast start in most areas for
beginning of holiday weekend. slow clearing to coast will mean
another 5-8 degrees of inland cooling on saturday...making it
coolest day of the week.
second half of weekend and holiday itself will feature a return to
stronger high pressure offshore feeding into developing low near
nevada/idaho border. north winds will rapidly ramp up off the coast
bringing drier/warmer flow to north bay valleys/mountains. more
organized trof of low pressure reaches pac nw sunday and may help
to disperse marine layer as heights fall slightly. more sunshine
should be had near the coast by late sun into memorial day but
thermal trof staying just inland will mean immediate beaches stay
cool and probably cloudy much of day. inland temperatures will
warm..but only approach near normal levels.
extended range forecast indicates continued near seasonable pattern
into middle of next week as thermal low progresses to near coast
with slackening onshore gradient...perhaps warming beaches a bit.
upper level heights/temperatures show no sign of extreme warming
however so inland will remain pleasant. by end of period model
solutions indicate various solutions in regards to possible cutoff
upper low off central/southern ca coast. no reason to hedge bet
either way at this time and extended range forecast continues
with generic pattern...similar to climatology for late may/early
june.
&&
.previous aviation...low clouds are starting to amass along the coast
but the marine layer depth remains fairly shallow...around 1000 feet
deep per the fort ord profiler data. the surface pressure gradients
continue to be moderate-to-strong northerly with 3.0 mb between acv
and sfo...and 4.8 from sfo-las. 2.3 mb between sfo and sac last
hour indicates an increasing onshore flow. expect an early ceiling
at monterey and salinas airports tonight...around 03z or 04z.
ceiling formation will be later at bay area airports given the
northerly flow...after midnight local time.
&&
.mtr watches/warnings/advisories
tngt...none
&&
public forecast: soroka
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 251041
afdmtr
area forecast discussion
national weather service san francisco ca
345 am pdt fri may 24 2007
updated aviation discussion
.discussion...fort ord profiler shows the marine layer is
still near 1000 feet and onshore flow persists with the sfo-
sac gradient at 2.4 mb. current satellite illustrates stratus along
the coast which is nudging into the golden gate bridge and moving
inland around the monterey bay...especially into the salinas valley.
the movement of stratus is from north to south as opposed to the
southerly surge from yesterday. the coamps model indicates the
possibility of brief and light southerly flow along the coast early
friday morning but only for a few hours and restricted to the
coastline south of point sur.
the intruding marine environment will keep temperatures similar to
slightly cooler than yesterday region-wide...cloudy coastal areas
ranging in the mid 50s to mid 60s...warmer inland temps ranging
from the mid 70s to lower 90s. this trend will continue into the
holiday weekend as no major changes in the weather pattern are
expected. the upper levels indicate fairly zonal flow with a subtle
trough approaching central california on saturday into sunday which
could deepen the marine layer and make stratus burn off a little
later.
ecmwf...gfs...and eta models forecast an approaching ridge moving
over the cwa monday afternoon and tuesday as 500 mb heights
increase a bit and should allow temps to warm about 3-5 degrees
between sunday and monday. beyond that...a closed low coming from
the subtropics will be spinning over the ocean to the southwest of
central california. it is progged to move into monterey and san
francisco bays late wednesday/early thursday then head north along
the coastline towards eureka. this is a change from model output the
past few days...however it has been consistent in the last few runs
of the above mentioned models. it should be noted that the ecmwf
indicates a weaker low that isn`t a closed system compared to the
other models. will monitor this longer range forecast to see if it
comes to fruition. if so...no rain is associated with this system
though it will probably enhance cloudiness and deepen the marine
layer.
&&
.aviation...increasing onshore flow overnight has brought stratus
across much of the san francisco bay area. the marine layer remains
shallow around 800-1000 feet...so ceilings are dropping into the ifr
category at oak...hwd and apc. continued westerly winds at sfo has
kept the stratus away so far...but the best model guidance indicates
that these west winds will slowly weaken and allow the stratus to
encroach upon sfo after approximately 13 utc. expecting the low
ceilings across the bay to scatter out at all terminals between 16
utc and 17 utc today.
&&
.mtr watches/warnings/advisories
tdy...none
&&
public forecast: bingaman
aviation/marine: brenchley
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 251808
afdmtr
area forecast discussion
national weather service san francisco ca
1100 am pdt fri may 24 2007
aviation update
.discussion...deeper penetration of stratus inland this morning as
marine layer deepened to about 15oo ft based on sfo and sql
sodars. expect fairly quick burnoff this morning as stratus decision
support tool and coamps 3 km run shows the bay clear by 16z.
bottom line is that san francisco will see cooler weather today
along with portions of the east and north bay that are in close
proximity to the bay. otherwise there has been little cooling
aloft. in fact 850 temps have warmed a few degrees since 00z last
night. so expect inland temps to be close to yesterday with the
coast seeing 5 to 10 degrees cooling and some inland valleys seeing
maybe 5 degrees of cooling where the marine air can intrude. looks
like zones have a good handle on this situation so no updates this
morning.
as a weak shortwave moves though the pacific nw into the northern
plains early next week will see an increase in the marine layer
tonight through early sunday. so inland areas should see more
cooling sat into sun. by sun night will see a weak offshore event
at least in the north and east bay which will push the marine layer
down and keep stratus near the coast overnight sun into monday.
latest nam indicates that this offshore event will be short lived
as onshore pressure gradients ramp up to almost 3 mb from sfo to
sac by 00z tue. given the holiday weekend will probably emphasize
this in our fire weather forecast this afternoon. temps will warm
on monday especially interior sections with the offshore flow. not
clear if coastal areas will see much warming as offshore flow may
not penetrate far enough east to push the marine air completely
offshore.
extended...looks like very typical summer pattern tue into later
parts of next week as weak ridge builds over the coast allowing the
establishment of a decent marine layer. thus expect seasonal temps
with cool at the coast and warm inland through the end of next
week. night and morning low clouds spreading locally inland
will be the rule. euro would indicate a more significant cooling
trend by the end of next week. but where and how close to the coast
the upper low it is forecasting will need to be watched. for now
will go close to climo for first week of june.
&&
.aviation...stratus penetrated well inland this morning. however
latest satellite imagery indicates it is well on its way to
completely retreating to the coast. bay area terminals have
scattered out at this hour with the exception of kmry and ksns
which are expected to clear out between 18-20z. an early onset of the
stratus is expected tonight at kmry and ksns while other bay area
terminals hold out until around midnight. winds will remain mainly
out of the west with the afternoon seabreeze kicking in around 20z.
&&
.mtr watches/warnings/advisories
tdy...none
&&
public forecast: reynolds
aviation/marine: c walbrun
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 252351
afdmtr
area forecast discussion
national weather service san francisco ca
445 pm pdt fri may 25 2007
updated aviation
.discussion...temperatures cooled off even more than expected
today...even in the interior sections of the forecast area. current
onshore gradient is 2.8 mb which is a good mb over yesterday at
this time. low clouds have hung along the coast and over san
francisco and monterey all day today. this has kept the city much
cooler than yesterday with the high so far today of 55 in
downtown. a much more typical near early june pattern for san
francisco. most other readings are down 5 to 10 degrees from
yesterday. do not see much reason not to continue and even increase
the low cloud penetration overnight with good onshore flow and 500 mb
heights continuing to fall slightly over the next 24 to 36 hrs.
latest 3 km coamps and 12 km nam show more widespread low level rh
tonight interior sections with a further increase by sunday morning.
so expect widespread overcast many areas sat and sun mornings with
clearing back to the coast by midday. temperatures will be near
normal or maybe slightly below normal through the weekend.
by sunday night a weak upper trough will have moved through the
pacnw allowing high pressure to build into or and nor cal setting
up a weak offshore flow sunday night into monday morning in the north
and east bay hills. do not expect this to amount to any serious
threat at this point. winds are not especially strong and humidities
drop but appear to be able to recover fairly quickly monday night as
models indicate a quick return to onshore flow. so out of this
three day weekend monday may be the best day of the three as far as
sunshine and warm temperatures...at least inland locations.
extended...weak ridging develops tue into wed over the area but the
surface pattern still shows an onshore gradient. so expect low
clouds and patchy fog to extend locally inland tue and wed nights
but not reach interior valleys. temperatures should be
seasonable. both the euro and the gfs show a weak cutoff developing
by thur into fri of next week which will deepen the marine layer and
allow deeper penetration of the low clouds and fog into interior
valleys by thur night into friday. temps will cool also by the
end of the week though interior valleys.
&&
.aviation...the marine layer has deepened to about 1700 feet per the
fort ord profiler and moderate onshore gradients are being observed
late this afternoon. both prevailing conditions and forecast
boundary layer rh indicate that ifr cigs will develop at kmry and
ksns by 02z with lcl lifr cigs at these terminals later tonight.
low clouds will likely develop earlier at ksfo and koak than
previously thought and 00z tafs reflect this will mvfr cigs forecast
to develop at both locations around 03-04z this evening with ifr cigs
likely after 06z. mvfr cigs are also likely at ksjc...but not until
late tonight. stratus will not scatter out until late saturday
morning around sf bay...and not until early afternoon near monterey
bay.
&&
.mtr watches/warnings/advisories
tdy...none
&&
public forecast: reynolds
aviation/marine: dykema
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 260551
afdmtr
area forecast discussion
national weather service san francisco ca
1045 pm pdt fri may 25 2007
update aviation
.discussion...stratus covers much of the coast south of bodega
bay this evening and is working its way inland into the coastal
valleys. latest ft ord and bodega bay profiler data show a marine
layer depth of about 1400 ft...while comparison with satellite
imagery from the same time yesterday evening shows enhancement of the
stratus field over the past 24 hours. as of 7 pm...the onshore
pressure gradient from ksfo to ksac had increased to 3.8 mb. max
temps this afternoon were cooler than on thurs...with the exception
of well inland and higher elevations locales uninfluenced by the
marine air. the high temperature in downtown san francisco was a
chilly 58 degs...well below the average for the date of 64.
some further deepening of the marine layer and strengthening of the
onshore flow are expected saturday as the tail end of a weak upper
level trough approaches our coast. as a result...daytime
temperatures are projected to remain on the chilly side near the
water...and continue to cool off inland. have just issued an
update...mainly to make some downward adjustments to tomorrow`s
highs.
not much change appears to be in store for sunday...with a deep
marine layer and cool onshore flow continuing. sunday night and
monday however...the upper level trough is projected to move
inland...with ridge development aloft off the west coast and surface
high pressure building inland through the pacific northwest into the
northern great basin. the resulting combination of subsidence and a
more offshore component to the lower tropospheric winds should then
diminish the marine layer and associated stratus and begin a warming
trend in daytime temperatures. this may prove to be short-lived
though...as longer range models bring the next weak upper level
trough westward towards the coast around midweek.
&&
.aviation...by late friday evening the marine layer was about 1500
feet deep according to the fort ord profiler. moderate onshore flow
continued. do not expect any significant change in either marine
layer depth or onshore flow overnight and thus ifr cigs will continue
through the night and into saturday morning with local mfvr/ifr vsbys
at ksts...kmry...and ksns. low cigs will not scatter out until late
saturday morning around sf bay...and not until early afternoon near
monterey bay. the marine layer is expected to deepen late saturday
and onshore flow will increase. the result will be an earlier onset
of mvfr cigs late saturday afternoon and evening.
&&
.mtr watches/warnings/advisories
none
&&
public forecast: blier
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 261141
afdmtr
area forecast discussion
national weather service san francisco ca
440 am pdt sat may 26 2007
updated aviation discussion
.discussion...the onshore flow has allowed widespread intrusion of
low clouds and fog...the eastern edge lies along santa rosa down
through livermore and concord...all around the monterey bay and deep
into the salinas valley. sfo-sac gradient is around 3 mb and the
depth of the marine layer is near 1500 ft.
overall...max temperatures should trend downward by a few
degrees. the nam model forecasts that the onshore gradient will
strengthen saturday during the day...closer to 4 mb which means
stratus will have a harder time burning off and should keep coastal
temperatures cool again with below normal temperatures...mid 50s to
mid 60s. farther inland...temps may nudge down a bit but should
remain on the warmer side...low 70s to low 80s...since the marine
layer has less influence.
models still agree that a very weak trough will pass over the region
on sunday which will help deepen the marine layer a tad and continue
the typical pattern of late night/early morning stratus. on monday
and tuesday a ridge will build and move inland over the cwa which
should cause some warming...especially inland...by about 2-5
degrees. this ridge precedes a storm brewing in the gulf of alaska
which will track towards canada...however...rain along the
associated surface front will stay well north of our region. the
upper level trough from this storm will be elongated well south
between 20-30n latitudes. the gfs continues to create closed lows
from the tail end of the trough. these lows move east towards the
west coast but the latest model runs have changed their track.
instead of heading right between sf and monterey bays...their path
now follows a more southern route towards los angeles and san
diego. if this holds true...the likely affects to central california
will be offshore flow and the possibility of clearing out coastal
stratus.
&&
.aviation...marine layer stratus continues to bring widespread ifr
conditions across the sfo and mry bay areas this morning. the top of
the marine layer stands near 1500 feet and with a moderate onshore
gradient...these ifr ceilings will be slow to scatter out today.
expect low ceilings at sfo bay terminals will begin lifting around 17
utc then clearing between 18 utc and 19 utc. the monterey bay area
terminals will scatter out later around 20 utc. the onshore
gradient is forecast to increase late this afternoon and evening
bringing low clouds back to the bay areas after 01 utc.
&&
.mtr watches/warnings/advisories
none
&&
public forecast: bingaman
aviation/marine: brenchley
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 261756
afdmtr
area forecast discussion
national weather service san francisco ca
1055 am pdt sat may 26 2007
.discussion...visible satellite imagery shows a typical morning low
clouds/fog intrusion into inland valleys throughout the cwa. the
marine layer depth is estimated at just over 2000 feet per the
fort ord profiler and the 12z oakland sounding. the surface pressure
gradient is moderate onshore with 2.3 mb between san francisco and
sacramento...and 5.7 mb from sfo to las.
the 12z run of the nam model indicates that the onshore flow will
increase during the day today as an upper level trough approaches
the coast. thus...cooler temperatures are anticipated today and
sunday across the district.
on monday high pressure aloft is forecast to build along the coast
with a brief offshore surface flow setting up across the hills
sunday and monday night. right now the 12z nam puts the strongest
winds at 925 mb across northern napa county early monday morning
with litter winds tuesday morning. the northerly or offshore gradient
is not progged to be super tight across our district but is
stronger across extreme northern california. warmer temperatures are
then expected early next week...especially inland areas.
the upper ridge is progged to build inland into the great basin by
midweek with another upper trough approaching the coast by the
weekend.
&&
.aviation...the marine layer remains around 2000 feet per the fort
ord profiler at this hour. satellite imagery shows the stratus
slowly withdrawing from the inland valleys and bay and is expected
to scatter out over the affected terminals between 19-21z. coastal
terminals such as kmry will be the last to clear. stratus is
anticipated to persist along the coast through the day with an early
return expected to be similar to last night. winds will remain out
of the west with the afternoon seabreeze kicking in around 21z mainly
affecting ksfo which will see gusts in the 20-25 kt range.
&&
.mtr watches/warnings/advisories
none
&&
public forecast: anderson
aviation/marine: c walbrun
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 262353
afdmtr
area forecast discussion
national weather service san francisco ca
455 pm pdt sat may 26 2007
updated aviation discussion
.discussion...satellite imagery shows low clouds and fog have cleared
back to near the coast in most places. everywhere except along the
san francisco peninsula and around the monterey bay have seen at
least a few hours of sunshine today. 24 hour temperature trends are
running warmer by a few degrees across many inland areas such as
oakland and san jose...while near-coastal sites as well as those
plagued by late-burning off stratus have been cooler...e.g. santa
rosa and monterey. the surface pressure gradient remains fairly
robust with 2.5 mb between sfo and sac...and 6.7 mb from sfo-las. the
marine layer depth has lowered some and now rests at about 1800 feet
deep.
models indicate that the onshore flow will maintain overnight and on
sunday as an upper level trough approaches the coast. thus...cool
temperatures are expected again on sunday across the district. by
monday high pressure aloft is forecast to begin building along the
coast with a brief offshore surface flow setting up across the hills
sunday and monday night. the latest run of the nam keeps the
strongest winds at 925 mb over northern napa county early monday
morning with lighter winds expected tuesday morning. the northerly
surface pressure gradient is forecast to be strongest across extreme
northern california and less so across our district. a slight warming
trend is indicated early in the week followed by a gradual cool-down
towards week`s end as another broad upper trough nears the west
coast.
&&
.aviation...the marine layer depth is currently about 1800 ft
as per latest data from the bodega bay and ft ord profilers.
satellite imagery shows stratus along all of the central california
coast and already beginning to push back inland around monterey bay
and through the golden gate and across to the berkeley hills. this is
slightly ahead of yesterday`s timing...and thus expect ceilings to
redevelop at ksfo by approx 0130z and koak by about 02z...and inland
to ksjc and ksts by around 05z. ceilings persisted throughout the day
at kmry and have now already returned to ksns. clearing times at
terminals tomorrow are projected to be similar to or a bit later
than today.
&&
.mtr watches/warnings/advisories...
.tngt...sca...sfo bay this evening.
&&
public forecast: anderson/dykema
aviation/marine: blier
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 270546
afdmtr
area forecast discussion
national weather service san francisco ca
1045 pm pdt sat may 26 2007
updated aviation discussion
.discussion...temperatures were generally below normal once again
today...most notably near the coast and in the coastal valleys...as
moderate onshore flow continued to usher cool marine air inland. the
marine layer...at a depth of about 1800 feet...was not deep enough
to allow marine air to reach the farthest inland valleys and
temperatures were still warm there with lower 90s common across
southern monterey county and san benito county.
water vapor satellite imagery shows a shortwave trough approaching
the pac nw this evening. the approach of this upper level
disturbance has intensified the inland push of marine air over the
past few hours. the fort ord profiler indicates that the marine layer
depth has recently increased to about 2200 feet. meanwhile...onshore
gradients have ramped up with the sfo-sac gradient up to 5 mb as of 8
pm. westerly winds have increased and are gusting in excess of 30 mph
from the golden gate to travis afb. given the deepening marine layer
and strong onshore flow...expect stratus to surge well inland
overnight and cover most of our cwa below 2500 feet by daybreak.
satellite imagery already shows that stratus has surged inland from
monterey bay nearly as far as the pacheco pass. given the robust
marine push underway...expect temperatures on sunday to be cooler
than today...especially inland. the forecast was updated this evening
to decrease high temperatures on sunday and to a lesser extent
monday...to increase cloud cover tonight and sunday...and to add
patchy drizzle for coastal areas tonight and sunday morning. expect
little...if any...clearing at the ocean beaches sunday afternoon.
by monday the upper level shortwave trough will have moved well
inland and the longwave ridge over the west coast will begin to
reassert itself. also...onshore low level flow will begin to
slacken. in fact...the nam shows winds at the 925 mb level turning
light offshore across the north bay by early monday morning. thus...
temperatures should begin to warm on monday...especially in the n
bay. warming will continue into tuesday as the upper ridge slowly
amplifies overhead. the marine layer will persist near the ocean...
but be compressed to a shallower layer...resulting in less nighttime
inland low cloud/fog development.
by midweek the gfs...and to a lesser extent the ecmwf...develops a
weak closed upper low off the southern ca coast...and then maintains
its position there and slowly deepens it through the end of the week
and into next weekend. this low is forecast to develop under the
longwave ridge and heights over our area will remain nearly steady
through midweek before climbing late in the week. the airmass aloft
is forecast to warm as easterly flow develops to the north of the
closed low. under this scenario...temperatures will continue to warm
for inland areas right on through the forecast period. if the
upper low develops as forecast by the gfs...offshore flow aloft may
trigger the development of a surface lee trough west of the coastal
ranges and produce light offshore surface flow...resulting in
significantly warmer coastal temps during the second half of the
week...especially across the southern portion of the district.
however...the ecmwf does not develop the upper low to the extent that
the gfs does and so will forecast only modest coastal warming for
now.
&&
.aviation discussion...ceilings have developed at all area terminals
except ksjc...and a ceiling is expected there before midnight. local
drizzle has been reported near the water. with the increase in depth
of the marine layer that`s occurred over the past day...ceilings and
visibilities are not running quite as low as 24 hrs ago. on the other
hand...the greater depth will also result in locally a bit later
clearing times tomorrow. onshore winds sunday afternoon are expected
to be similar to today.
&&
.mtr watches/warnings/advisories...
.tngt...sca...pt arena to pigeon pt and sfo bay.
&&
public forecast: dykema/reynolds
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 271110
afdmtr
area forecast discussion
national weather service san francisco ca
410 am pdt sun may 27 2007
updated aviation discussion
.discussion...fog and low clouds have spread well inland overnight
with measurable drizzle observed along monterey bay and most likely
along most county coastal sections from sonoma to monterey. marine
layer is a healthy 2000 ft this morning. onshore gradients at 3.3
mb from sfo to sac and travis is blowing at 25 to 35 mph. thus
strong marine push inland. expect high temperatures today to be at
or maybe even a few degrees cooler than yesterday given strong
marine push and more extensive low clouds. looks like today will be
the cloudiest and coolest of the holiday weekend. models are
indicating a shallower marine layer by monday as 500 mb heights
begin to build behind weak upper trough that will be moving east
into the northern great basin.
so after monday looks like interior sections will begin to warm as
ridging takes place over the west coast. typical summer pattern
will develop with about a 1200 ft marine layer with night and
morning coastal low clouds spreading locally inland but generally
limited to coastal valleys.
extended...models have been trying to get a handle on weak upper
low that forms off the west coast by mid week. both the euro and gfs
have some semblance of a high to the north of ca and a weak upper
low somewhere in so cal. the combination of the two developers a se
flow aloft which will bring in warm air from the desert southwest.
850 temps are forecast to rise to 22 to 23 c by thursday. this will
help warm interior temperatures into the upper 80s to mid 90s with
near temperatures near 100 warmest interior sections of sonoma and
napa counties and southern monterey county. coastal sections will
warm slightly as low clouds will burn back off the coast each day
before noon providing more abundant afternoon sunshine. as the upper
low moves east by late friday may see slight deepening of marine
layer and cooler interiors by saturday. low clouds and fog will
begin to spread further inland overnight fri aiding the expected
cooling trend.
&&
.aviation discussion...all terminals have ifr conditions this morning
except ksjc which has mvfr. expect that the breakout to vfr
conditions will not occur til 19z at ksts and ksjc...20z at ksfo and
koak...21z at ksns...and 22z at kmry.
&&
.mtr watches/warnings/advisories...
.tdy...sca...pt arena to pigeon pt out 60 nm.
&&
public forecast: reynolds
aviation/marine: strobin
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 271805
afdmtr
area forecast discussion
national weather service san francisco ca
1105 am pdt sun may 27 2007
aviation update
.discussion...visible satellite imagery shows the coastal stratus
has penetrated well inland into all inland valleys this morning. the
marine layer has ramped up to about 2500 feet...and the surface
pressure gradients continue to the moderate to strong onshore with
3.0 mb between sfo and sac...5.7 mb from sfo-wmc...and 6.7 mb from
sfo to las. cool temperatures are expected today district-wide as a
broad upper trough moves across the pacific northwest and the deep
marine layer influences our immediate area. max temps today will
struggle to get out of the 60s in most areas except the warmest
interior locations that may make it into the lower 80s.
an upper ridge is forecast to briefly build over the west coast
beginning on monday and building towards the great basin early in
the week. this will serve to flatten the marine layer somewhat as
well as bring about a brief and weak offshore flow monday morning.
temperatures are expected to warm through midweek with inland areas
getting back up into the 90s by thursday.
the upper ridge is progged to move east by next weekend with another
broad upper trough approaching the coast. this would once again ramp
up the marine layer by the weekend with cooling onshore flow.
&&
.aviation...ceiling across bay area terminals have lifted and are
expected to scatter out by 19z. vfr conditions are expected through
the rest of the day. kmry may not clear at all today while ksns is
expected to clear out between 19-20z. winds will pick up once again
this afternoon at ksfo with winds in the 15-20 kt range with gusts
to 22 kt.
&&
.mtr watches/warnings/advisories...
.tda...sca...pt arena to pt piedras blancas and sfo bay.
&&
public forecast: anderson
aviation/marine: c walbrun
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 272335
afdmtr
area forecast discussion
national weather service san francisco ca
435 pm pdt sun may 27 2007
update aviation discussion
.discussion...satellite loops show the coastal stratus eroding from
the north with completely clear skies gracing the north bay at this
time...as well as all inland areas of the cwa except for around the
san francisco bay and the monterey bay. 24hr temperature trends are
running cooler by several degrees at most locations except for
across the southern third of the district where several degrees of
warming have been noted. afternoon temperatures are ranging from the
mid 50s at the immediate coast to the 60s and 70s inland. the
interior reaches of monterey and san benito counties have warmed to
the mid 80s thus far today.
a moderate onshore flow persists with a 2.9 mb surface pressure
gradient between sfo and sac sustaining 20g26 kt winds at travis
afb and sfo from the west. the surface pattern is forecast to shift
to a more northerly direction overnight per the latest nam and gfs
models as a surface high builds into the pacnw and the northern
great basin while low pressure lingers over the interior of
california. although the tightest gradient is expected to remain
across the extreme northern portion of the state...locally gusty
northeasterly breezes are possible across the higher hills of the
north and east bay areas by monday morning. this offshore flow is
progged to be short-lived...however...as the flow returns to
onshore by tuesday.
high pressure aloft is forecast to build in over the west coast on
monday and tuesday before shifting eastward into the great basin
after midweek. thus...a slight warming trend is indicated through
midweek with somewhat less stratus coverage...followed by a
gradual cooling trend and more inland stratus over the weekend.
&&
.aviation...the northerly surface gradient down the coast from acv
to sfo has increased to 4.3 mb late this afternoon and this has
resulted in coastal clearing as far s as the marin county coast. but
satellite indicates the clearing trend along the coast is ending and
with a 3.6 mb onshore gradient from sfo to sac...expect mvfr cigs to
develop at ksfo by 03z with all terminals near sf bay expected to
develop mvfr cigs by 06z. the moderate northerly gradient will keep
ksts clear through at least 08z. further s...kmry and ksns will
maintain mvfr cigs through the night...temporarily dropping to ifr
late tonight. the marine layer...currently at a depth of about 2100
feet per the fort ord profiler...should compress somewhat overnight.
a shallower marine layer combined with a light north to northeast
wind aloft forecast to develop by late tonight per the latest nam
should result in earlier clearing on monday than what has occurred
the past two days.
&&
.mtr watches/warnings/advisories...
.tngt...sca...pt arena to pigeon point and sfo bay.
&&
public forecast: anderson
aviation/marine: dykema
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 280547
afdmtr
area forecast discussion
national weather service san francisco ca
1050 pm pdt sun may 27 2007
updated aviation
.discussion...maximum temperatures today were generally 2-10 degrees
cooler than yesterday with the biggest cooling trend farther inland.
not much change expected in overnight lows this evening...the typical
range around 45-55 degrees. however tomorrow`s max temps should trend
up at least a couple degrees along the immediate coastline and 5-10
degrees elsewhere as an upper ridge begins to affect the region.
a moderately deep marine layer between 2000-2500 ft has persisted for
the past 24 hours as an upper level trough is moving east over the
region. though this trough enabled widespread stratus earlier
today...the northerly gradient from arcata to sfo jumped over 6 mb
recently which has boosted winds over the northern coastal waters and
aided in clearing stratus around sf and monterey bays. surface high
pressure offshore from the oregon coast now reaches inland north of
california allowing the enhanced north-south gradient. however...the
nam model output indicates that this northerly push will weaken by
monday morning as the onshore gradient from sfo to sacramento becomes
the more prominent factor in wind flow at 3 to 5 mb. onshore flow
will dominate the surface wind pattern through the period.
the upper trough will continue moving east overnight as a ridge
develops offshore from the west coast. by 18z (11am pdt) monday
morning the central california coast will be under the right side
of this ridge. the ridge should affect the west coast through
wednesday as the axis moves directly over our cwa on tuesday and
then moves to the east wednesday night into thursday. its influence
at the surface will bring warmer temperatures and a drier airmass as
the marine layer gets compressed down to 1000-1500 feet. patchy fog
and low clouds will continue to form in the early morning hours but
a shallower cloud deck will likely cause earlier burnoff times
compared to the past few days for most of this week. long range
models indicate an upper level trough moving over the region by the
end of the week which could enhance the marine layer again...
thicken the stratus deck and drop temperatures.
&&
.aviation...a strong northerly surface gradient from acv to sfo
allowed drier air to mix into the boundary layer along the n coast of
ca late this afternoon and resulted in clearing n of the golden gate.
this gradient also prevented widespread stratus from developing in sf
bay and the n bay valleys this evening. the n-s gradient has begun to
ease and models indicate further decreases overnight. as the gradient
drops off...mvfr/local ifr cigs will slowly develop around sf bay
overnight. ksfo and koak should see low cigs by 12z. low cigs are
less likely at ksts and ksjc...but possible for at least a few hours
late tonight through mid morning on monday. the nam continues to
forecast the development of a light northeast flow at 925 mb by late
tonight. this should result in earlier clearing on monday morning
than what has occurred the past few mornings. anticipate low clouds
clearing from around sf bay by 17z. further s...at the mry bay area
terminals...onshore flow will be more persistent and low clouds
likely won`t scattered out until sometime between 18z and 20z.
&&
.mtr watches/warnings/advisories...
.tngt...sca...pt arena to pigeon point and sfo bay.
&&
public forecast: bingaman
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 281057
afdmtr
area forecast discussion
national weather service san francisco ca
400 am pdt mon may 28 2007
.discussion...satl imagery indc a weak trough passing across the
district early this morning. however...it has not had much affect
on the marine layer...which is near 2000 feet per the ft ord
profiler. fog product imagery indc an increasing area of stratus
across the district and down the salinas valley to paso robles. the
main effect of the trough passage has been the ramping up of the
northerly gradient between arcata-sfo which is 5.1 mb compared to 2.0
yesterday morning. the onshore gradient between sfo-sac has relaxed
to 1.7 mb compared to 3.4 mb yesterday morning.
with the increasing northerly gradient as a ridge builds into the
west coast temps should increase significantly today in the inland
locations...while the coast remains cool. little change in the
pattern is expected through at least mid week with a ridge over the
coast. the marine layer should flatten to near 1500 feet...but with
the surface thermal trough inland the coast will remain cool.
increasing 850 mb temps should keep inland temps near normal...mainly
in the 70s to upper 80s...with 90s in the southern interior sections
of monterey and san benito counties.
during the end of the week and into the weekend a trough will edge
closer to the coast as the ridge becomes centered over the
intermountain west. this should deepen the marine layer a bit...
keeping temps cool along the coast. inland areas should remain near
seasonable levels...70s and 80s with 90s in the southern interior.
basically typical summer weather for the next week.
&&
.aviation...tricky morning for terminals with moderate marine layer
depth and changes occurring in coastal gradients. stronger north
flow down coast should help dry things out quicker today as marine
layer shallows a bit...helping ceilings to clear bay area terminals
around 18z. lighter flow to the south could mean more stubborn
stratus around monterey bay til around 20z. onshore flow is weaker as
well...meaning afternoon winds at sfo should not be too significant.
expect evening clearing to linger into early part of tonight before
light south flow up to the coast brings ceilings back into the
terminals after 07z tue.
&&
.mtr watches/warnings/advisories...
.tdy...sca...pt arena to pigeon point.
&&
public forecast: strobin
aviation/marine: soroka
Scott Hazen Mueller
area forecast discussion
fxus66 kmtr 281717
afdmtr
area forecast discussion
national weather service san francisco ca
1000 am pdt mon may 28 2007 ... memorial day
.discussion...overnight stratus penetrating relatively deep in the
southern counties of the central coast forecast area. monterey
bay area and salinas valley covered completely along with all of the
southern portions of the santa clara valley. stronger n-s acv-sfo
pressure gradient of 3.4mb this morning vs. 2.5mb 24 hrs ago with
weaker onshore gradient through the s.f.bay area has cleared stratus
inland north of s.f. just after dawn and through much of the bay by
10 am. no change in temperatures or sky cover forecasts this morning
package.
in the short term night/morning stratus and clearing in afternoon
looks fine for coastal sections but based on height rises some upward
adjusting in inland temps needs to be made for wednesday and then
hold for thursday. no other changes made for this mornings forecast
package. of forecast concern...however...is the development of a weak
upper low progged off the south-central calif coast by wednesday
afternoon. besides providing warm low-level southerly flow over the
forecast area for temperatures...medium range models keep the low in
that vicinity to saturday. while vertical velocities appear weak the
time length of the lows presence could provide a moisture field with
continued convergent uplift. that moisture combined with low-level
heating would de-stabilize and lead to some isolated afternoon
convection over the south-interior mountains as early as wednesday
late afternoon. if the current model run verifies and the solution
to maintain the low in the same general area then thursday and friday
afternoon and early evening would have some isolated cells due to the
aforementioned instability. too soon to make any changes in the
forecast package and another model run is needed to look for
consistency in the upper low development.
&&
.previous aviation...tricky morning for terminals with moderate
marine layer depth and changes occurring in coastal gradients.
stronger north flow down coast should help dry things out quicker
today as marine layer shallows a bit...helping ceilings to clear bay
area terminals around 18z. lighter flow to the south could mean more
stubborn stratus around monterey bay til around 20z. onshore flow is
weaker as well...meaning afternoon winds at sfo should not be too
significant. expect evening clearing to linger into early part of
tonight before light south flow up to the coast brings ceilings back
into the terminals after 07z tue.
&&
.mtr watches/warnings/advisories...
.tdy...sca...outer waters pt arena to pigeon point.
&&
public forecast: gudgel
aviation/marine: bingaman