Models Revving Up For Mid-Atlantic... <1/4>
A.K. Cruiser
Perhaps many folks in the Mid-Atlantic have had the opportunity to use
their snow shovels once or twice already this year, but for most of us in
the RIC-DCA-BWI corridor we haven't had the need. It's been 10 or 11
months since I used mine, but, if the models have any clue this go around,
I'd better find it!! New England is less of a bet on this upcoming system,
it depends on what model you buy into. As for the Mid-Atlantic Friday
event, that looks to be generally a flurry system, so my energies will be
concentrated on the Sat-Mon storm situation. Time is a bit short for me
today and I have massive quantities of info to discuss, so let's get right
to it...
ETA: The short range models provide the "set-up" for the upcoming event
and may clue us in on which long-range model is starting up the best.
By 48hrs the ETA has an inverted trof from E LA NEward into E KY. The
precip shield extends up to much of WV, VA, and NC with only N & E
portions of the states not into precip by then. Most of this would be
in the form of snow with heavy amounts beginning to fall across the S
Appalachians. The vort ultimately responsible for further development
is swinging through TX/OK. Of importance is the 500mb flow which
indicates that precip should continue making Nward progress while
heading E... at least up to the PA/MD & PA/NJ/DE borders (this assumes
no further development which is likely a poor assumption). Also, much
of the confluent flow is offshore which will allow the system to NOT
get ripped apart until after it is offshore.
NGM: The NGM is a hair slower than the ETA with its development and
progression of things. By 12Z Sat it has an inverted trof from SE LA
up to SE TN with a low embedded in S AL. Precip by that point extends
into NE TN. The NGM upper flow is slightly flatter than the ETA.
While the differences are subtle, this would favor a less developed,
more progressive storm... though most of WV/MD/VA/DE should still get
well into the precip shield.
AVN: The AVN manages to take us deeper into the storm scenario. By 48hrs
it has the inverted trof from SW LA NEward to SC TN. This is similar
to, but a tad slower than, the ETA. At that point precip has spread
into E KY, S WV, SW VA, and W NC. Then by Sat evening a low, oriented
SSW to NNE is across the SE. Precip by then has reached extreme SW
PA and most of MD southward. Moderate snows would be occurring from
S WV, through SW VA, and into W NC. By Sun AM coastal cyclogenesis is
just getting underway with a 1006mb low near ILM. The upper flow is
buckling nicely and moderate to heavy snow has fallen across MD, DE,
VA (away from the immediate coast), and inland NC. Lighter snows have
reached as far N as N PA, S NY, and SW New England. That's the final
period on the AVN. However, given the storm motion and the buckling
occurring at upper levels I believe the implication would be that SE
New England would get a period of light snow as well (VVs imply the
best dynamics head out to sea south of New England).
MRF: As usual, I've generally overridden the MRF with the 12Z AVN, but so
so as to compare let's glance at the MRF. By Sat eve it has a weak
(but intensifying) low over C GA. This is a bit faster than the newer
AVN (or should I say, the new run is a bit slower). From there it
brings the low to HAT by Sun AM and then races it NE to well E of Cape
Cod (too far for any precip) by Sun eve. Oddly enough it still pumps
out almost an inch (about .8" to .9") liquid across most of VA, MD,
and DE (this is actually a bit more than the newer, slower AVN).
ECMWF: The EC is the destructo-model for this storm. It has, by Sat AM,
the inverted trof from SW LA to SE TN (and AVN/ETA compromise). Then
by Sun AM is has a NNE/SSW oriented low on the C GA/C AL border. Once
again this is in excellent agreement with the AVN, except that the AVN
is faster (getting the low to this point some 12hrs faster). By Mon
AM the low is bombing only 50-100mi E of the New Jersey coastline. It
finally pulls off into Nova Scotia by Tue AM. Precip type actually
comes into question from the Jersey coast to Long Island to extreme SE
New England. There the snow may mix with rain at the height of the
storm. Elsewhere (even SW toward DE, MD, and VA) the precip type is
most definitely snow.
UKMET: The UK is also quite slow. By Sat PM it has a weak wave off of SC,
but the main culprit is buried down in Mexico! It emerges into the
Gulf and off the GA coastline by Sun PM. Finally, it bombs and moves
NE to well E of Cape Hatteras. This would confine the best snows to
NC, VA, and perhaps WV, MD, and DE. Light snow would be possible to
extreme S PA and S NJ.
Other models: No time to get deeply into the other models, but here's a
point of interest. Both the NORAPS and UW-NMS show a preliminary
small event coming from the Gulf and scooting across the Mid-Atlantic
on Sat. This delays (or precludes??? it's unclear) the main event.
Precip from the preliminary low is light and somewhat insignificant
(generally 1" or less). This looks slightly similar to the UK. The
Canadian model is similar and develops this early system in lieu of
the second one. As such it has a low centered over SC by Sat night;
it hauls NE to well S of Cape Cod by Sun night. Still, precip in the
Mid-Atlantic is not insignificant. It is just a moderate instead of a
major snowstorm and occurs about 12hrs sooner.
NWS: Just a quick note on the local (DC) NWS. I don't know what they're
thinking. The latest forecast from them is calling for a chance of
snow Sat & Mon, but only mostly cloudy Sun!! It seems to be quite
obvious by the above models that Sunday is the most threatened day!
My thinking: Well, every last one of the several models presented here are
going for some type of a snow event in the Mid-Atlantic. Three critical
questions must be answered... How much? When? How far north does it get?
All three of these questions are meainly a function of the amplitude of the
developing pattern. The short range operational models are converging on a
solution between the MRF and ECMWF (which in the long term is much closer
to the EC since the latest MRF is much closer to the EC than the previous
MRF run). All of the short range non-operational models and the Canadian
operational model are all pointing toward a lead-shortwave event where Sat
aft into very early Sun instead of late Sat through midday Sun becomes the
focus of the event. For the third question we've got the UK which may have
trouble pushing precip as far N as the PA/MD border; and then there's the
EC which takes the whole storm full force into New England. Which such a
vast array of solutions and possibilities one might think this is another
impossible forecasting event. However, I find it easier than previous
events for two reasons: 1) Every model is calling for snows for VA, WV, MD,
and DE... it's just the scope and timing that are of concern; 2) The models
...even some of the non-operational ones... have been converging on an EC/
MRF solution. Given that the AVN is an EC/MRF solution, but the ETA/NGM
seem to be leaning a bit toward the MRF, I'm going with an EC/MRF blend
shaded toward the MRF. This means amount-wise we're looking for heavy snow
accumulations from inland NC to VA (away from the coast) and into S MD. A
decent swath of moderate snows would surround that in W VA, WV, N MD, and
DE. Light snows should spread as far N as C PA and C NJ. As the low pulls
NE light snows may also spread across SE New England. I'm not going to pin
exact numbers yet on "light", "moderate", and "heavy", but if it helps I
USUALLY consider light = 1-3", moderate 4-8", and heavy 8-12". Timing
looks to be entering extreme SW parts of the Northeast by late Sat aft and
spreading NE into DE (and S NJ) by early Sun AM. One of my primary
concerns is the forecasted very cold atmosphere... this could push snow
totals up and, while this type of snow MAY easily compact the breezy (NOT
windy) conditions behind the storm could keep things loose and cause some
of the typical blowing snow problems.
You should know that my confidence on timing, amounts, and the evolution of
this system is still fairly low and you should check back for updates.
However, given model convergence, my confidence in actually seeing a Sat/
Sun snowstorm across at least inland NC, inland VA, E WV, MD, and DE. But,
anyone who lives in this area knows the frequency with which things can go
wrong with the forecasted snow events, so stay tuned!!
-Gary