Mon Dec 7 Meteorology for Chicago
Brett Crapser
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1139 AM CST MON DEC 7 2009
DISCUSSION...
334 AM CST
TODAY...THE LIGHT SNOW WILL CONTINUE THROUGH THE MORNING.
THE RADAR AND SURFACE DATA SHOWS LIGHT SNOW ACROSS MOST OF NORTH
CENTRAL ILLINOIS...NORTHEAST ILLINOIS AND NORTHWEST INDIANA. THE
IR SATELLITE IMAGERY SHOWS COLD CLOUD TOPS OVER MICHIGAN. THIS IS
WHERE THE MOISTURE HAS BEEN LIFTED TO 27000 FEET. THERE IS A LOT
OF UPWARD VELOCITY WITH THIS SYSTEM. THE SURFACE LOW HAS MOVED INTO
EASTERN MISSOURI. THE TROUGH WAS FROM THE SURFACE LOW TO CENTRAL
LAKE MICHIGAN. THE SNOW WILL CONTINUE AS THIS TROUGH WILL BE AROUND
THIS MORNING AND THE 700 MB TROUGH OVER WESTERN MINNESOTA WILL
MOVE THROUGH THIS MORNING. WE EXPECT LESS THAN AN INCH IN MOST
PLACES. BY THE AFTERNOON. THE SURFACE TROUGH WILL MOVE EAST WITH
700 MB TROUGH AND THE SNOW WILL END IN OUR AREA.
TUESDAY THROUGH WEDNESDAY... WE WILL KEEP THE WINTER STORM WATCH I
N EFFECT. THE GFS...NAM AND THE ECMWF HAVE THE STRONG SURFACE LOW
OVER SOUTHERN LAKE MICHIGAN BY WEDNESDAY MORNING. THE SNOW AMOUNTS
WILL BE LARGER NORTHWEST OF A LINE FROM CHICAGO TO MENDOTA. SOUTH
AND EAST OF THE LINE WE EXPECT RAIN AND SNOW MIXTURE CHANGING TO
SNOW BY WEDNESDAY AFTERNOON. WE WILL ADJUST THE SNOW LINE SOUTH
THIS MORNING. THE WARM AIR ADVECTION ON THE SOUTHEAST SIDE OF THIS
STRONG SURFACE LOW MAY BE FARTHER EAST.
WEDNESDAY NIGHT THROUGH THURSDAY...THE WIND WILL INCREASE TO
25 TO 30 MPH WITH GUSTS TO 40 MPH. THERE WILL BE SOME BLOWING
SNOW ESPECIALLY IN OUR NORTHWEST COUNTIES. VERY COLD AIR WILL MOVE
INTO NORTH CENTRAL ILLINOIS...NORTHEAST ILLINOIS AND NORTHWEST
INDIANA THURSDAY.
&&
AVIATION...
1130 AM CST
1800 UTC TAFS...MAIN CONCERN FOR THE NEXT SEVERAL HOURS WILL FOCUS
LARGELY ON CEILINGS. THE AREA OF SNOW THAT IMPACTED THE REGION
OVERNIGHT AND THIS MORNING HAS MOVED OFF TO THE EAST. A WEAK MID
LEVEL IMPULSE IS MOVING DOWN THE LENGTH OF LAKE MICHIGAN AND SOME
ISOLD REPORTS OF -SN REMAIN...BUT ANY RESIDUAL SNOW SHOULD BE OF NO
OPERATIONAL IMPACT FOR THE REMAINDER OF THE AFTERNOON. CIGS
CONTINUE TO BE A MIXED BAG OF LOWER MVFR AND HIGHER END IFR UNTIL
LATE THIS AFTERNOON WHEN A MID LEVEL TROUGH MOVES OFF TO THE EAST
AND WEAK UPPER LEVEL RIDGING BUILDS IN.
THE FOCUS WILL QUICKLY SHIFT TO THE DEVELOPING WINTER WEATHER
SITUATION. THE LATEST GUIDANCE SUGGESTS THAT A STRONG WARM
ADVECTION PATTERN WILL SET UP THIS EVENING AND STRENGTHEN
OVERNIGHT. EXPECT THAT LIGHT SNOW WILL BEGIN DURG THE EARLY
MORNING HOURS. STRONGER FORCING WILL MOVE OVER THE REGION IN TIME
FOR THE MORNING RUSH HOURS AND EXPECT THAT CONDITIONS WILL
DETERIORATE RAPIDLY...WITH IFR CIGS/VIS DEVELOPING BY 12-13Z...AND
CONDITIONS SHOULD REMAIN IFR THROUGH THE REMAINDER OF THE
PERIOD...INCLUDING THE EXTENDED 30 HOUR FORECAST FOR ORD. EXPECT
THAT THE PCPN TYPE WILL BE ALL SNOW THROUGH WEDNESDAY AFTERNOON
AND EVENING.
THERE IS STILL SOME QUESTION IF THE PCPN WILL REMAIN ALL SNOW AT
ORD/MDW/DPA...PARTICULARLY LATE EVENING HOURS TOMORROW NIGHT. THE
EXACT TRACK OF THE SYSTEM WILL BE CLOSELY MONITORED AS ONLY SLIGHT
VARIATIONS IN THE TRACK OF THE MAIN SURFACE LOW AND MID LEVEL
CIRCULATION COULD HAVE A SIGNIFICANT IMPACT ON PCPN TYPE AT
ORD/MDW/DPA. AT THIS POINT HOWEVER...EXPECT THAT RFD WILL REMAIN
ALL SNOW FOR THE DURATION AND THE EVENT AND GYY WILL SEE A
PERIOD OF A CHANGE-OVER TO RAIN.
KREIN
&&
MARINE...
345 AM CST
GALE WATCH EXPANDED TO ENTIRE LAKE WITH START TIME MOVED UP TO TUE
NIGHT AS WELL AS LENGTHENED INTO LATE THU NIGHT.
WEAK LOW IN NORTHEAST MO TO MOVE NORTHEAST AND ACROSS SOUTHERN
LAKE MI AND CENTRAL LOWER MI DURING THE MORNING.
POTENT LOW TO TRACK NORTHEAST ACROSS THE MID MS VALLEY TUE NIGHT
AND BE NEAR OR OVER SOUTHERN LAKE MI BY WED MORNING. GALES ON THE
LAKE A GIVEN BUT WITH SOME DIFFERENCES IN TRACK OF THE LOW BETWEEN
VARIOUS MODELS TIMING IS A QUESTION. SFC LOW POSITIONS AT 12Z WED
BASED ON SFC WIND STREAMLINES VARY FROM BETWEEN VPZ AND SBN PER
FURTHEST SOUTH GFS ENSEMBLE CLUSTER AND MEAN...TO JUST SOUTH OF
SBM PER FURTHEST NORTH NAM. BEST GUESS AT THIS TIME IS FOR LOW TO
REACH WESTERN SHORE OF THE LAKE AT OR A BIT NORTH OF THE WI STATE
LINE.
HIGH POTENTIAL FOR GALES ON VARYING PORTIONS OF THE LAKE AHEAD OF
THE APPROACHING DEEPENING LOW TUE NIGHT AS WELL AS WHILE IT
CONTINUES TO DEEPEN AS IT LIFTS NORTHEASTWARD THROUGH THE CENTRAL
GREAT LAKES WED AND INTO SOUTHERN QUEBEC WED NIGHT.
TRS
&&
LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
ILZ011-ILZ012-ILZ019...6 PM TUESDAY TO 7 PM WEDNESDAY.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-
LMZ874-LMZ876-LMZ878...9 PM TUESDAY TO 2 AM FRIDAY.
&&
$$