FXUS63 KLOT 061736
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1136 AM CST SUN DEC 6 2009
.DISCUSSION...
206 AM CST
THERE WILL BE SNOW TONIGHT MOST OF WHICH WILL FALL IN THE NORTH
HALF OF OUR FORECAST AREA. ANOTHER LOW WILL PRODUCE SNOW TUESDAY
THROUGH WEDNESDAY.
TODAY AND TONIGHT...THE 300 MB JET STREAM IS OVER ILLINOIS.
THE JET STREAM WILL MOVE EAST TODAY. THERE WAS A SOUTH WIND OVER
ILLINOIS THIS MORNING. THE PROFILER AT WOLCOTT INDIANA SHOWS THE
WIND VEERING WITH HEIGHT. THIS WARM AIR ADVECTION WILL INCREASE
THE VORTICITY AT 925 MB AND INCREASING THE STRENGTH OF THE COLD
FRONT THAT LIES FROM WISCONSIN TO THE OKLAHOMA PANHANDLE. BY
THIS EVENING THE FRONT WILL BE A STRONG ENOUGH BAROCLINIC ZONE TO
SUPPORT A CYCLONE OVER NORTH CENTRAL ILLINOIS BY MONDAY MORNING. A
SHORT WAVE OVER NEVADA THIS MORNING WILL MOVE INTO ILLINOIS
MONDAY. MORNING. ANOTHER 300 MB JET STREAM WILL SPREAD OVER
ILLINOIS MONDAY MORNING. THIS WILL BE A SHORT LIVED EVENT. THE LOW
IS FORECAST TO MOVE QUICKLY. THE NAM...GFS...SREF AND ECMWF SHOW
THIS TO BE A WEAK LOW. WE WILL FORECAST 1 TO 2 INCHES OF SNOW.
THERE IS FORECAST OMEGA OF AROUND -3 MB/S DUE TO ISENTROPIC LIFT
FROM THE NAM MODEL. THE SOUNDING FORECAST HAS SIGNIFICANT MOISTURE
WITH A ONE DEGREE SPREAD AT 800 MB FOR EARLY MONDAY MORNING. WITH
A 12 TO 17 DEGREE TEMPERATURE FROM 1700 METERS TO 3300 METERS WE
EXPECT SOME DENDRITE SNOW CRYSTALS. THE SREF AND NAM MODELS ARE SIMILAR
IN THIS FORECAST. WE WILL FORECAST HIGH TEMPERATURES IN THE MIDDLE
TO UPPER 30S AND LOW TEMPERATURES IN THE MIDDLE TO UPPER 20S
TONIGHT.
MONDAY THROUGH TUESDAY NIGHT...MONDAY AND MONDAY NIGHT THE WEATHER
WILL BE DRY. THE NEXT CYCLONE WILL DEVELOP IN OKLAHOMA IN THE
BAROCLINIC ZONE OF THE SOUTHERN JET STREAM. COLD AIR WILL BE IN
PLACE OVER NORTH CENTRAL ILLINOIS AND NORTHWEST INDIANA. A 500 MB
LONG WAVE TROUGH IS FORECAST TO MOVE INTO THE CENTRAL PLAINS. THE
LONG WAVE TROUGH IS FORECAST TO CHANGE ITS ORIENTATION AS IT MOVES
INTO THE MISSISSIPPI VALLEY. WE EXPECT THE CYCLONE TO DEEPEN AND
MOVE INTO NORTHERN ILLINOIS OR NORTHERN INDIANA BY WEDNESDAY
MORNING. THIS COULD BE A SIGNIFICANT CYCLONE WITH HEAVY SNOW. WE
WILL NOT ISSUE A WINTER STORM WATCH AT THIS TIME. WE WILL WAIT TO
SEE WHERE THE CYCLONE WILL TRACK. WE WILL ADJUST THE PRECIPITATION
TYPE A LITTLE BASED ON A COMPROMISE OF THE GFS AND NAM WITH THE
SREF AND ECMWF MODELS. THIS STORM WILL BRING SIGNIFICANT WIND AS
WELL. THERE MAY BE BLOWING AND DRIFTING SNOW. THE SOUTHEAST
COUNTIES MAY HAVE RAIN AND SNOW MIXED BEFORE TURNING TO ALL SNOW
BY WEDNESDAY MORNING.
WEDNESDAY THROUGH THURSDAY...THE SNOW WILL MOVE OUT WEDNESDAY NIGHT.
EXTREMELY COLD AIR WILL MOVE TO NORTHERN ILLINOIS AND NORTHWEST
INDIANA...AS A BIG HIGH MOVES INTO THE MISSISSIPPI VALLEY
THURSDAY. WE MAY HAVE LOW TEMPERATURES IN THE SINGLE DIGITS AND
HIGH IN THE LOWER 20S.
&&
.AVIATION...
18Z TAFS...MAIN FORECAST CONCERN THIS PERIOD IS SNOW POTENTIAL
LATE TONIGHT INTO MONDAY MORNING ALONG WITH ASSOCIATED CIGS/VIS.
A WEAK COLD FRONT WILL SLOWLY MOVE SOUTHEAST ACROSS THE WESTERN
LAKES REGION THIS AFTERNOON AND TONIGHT. AS IT DOES...AN AREA OF
WEAK LOW PRESSURE WILL MOVE NORTHEAST ALONG THIS FRONT MONDAY
MORNING. SOUTHERLY WINDS WILL CONTINUE TO DIMINISH THRU THIS
EVENING AND POSSIBLY BECOME LIGHT AND VRB OVERNIGHT INTO MONDAY
MORNING AS THE GRADIENT BECOMES RATHER WEAK. AS THE LOW LIFTS
NORTHEAST AWAY FROM THE AREA MONDAY AFTERNOON...THE COLD FRONT
WILL SWING THRU THE AREA WITH WINDS TURNING WEST THEN NORTHWEST.
LOW LEVELS ARE QUITE DRY AND REMAIN DRY THRU LATE THIS EVENING
WHILE SLOWLY SATURATING OVERNIGHT. THUS EXPECT SNOW TO BEGIN
FIRST AT RFD THEN SPREAD NORTHEAST ACROSS THE REST OF TERMINALS
TOWARD MONDAY MORNING. HOWEVER...BULK OF THIS LIGHT SNOW SHOULD
REMAIN NORTHWEST OF THE TRACK OF THE LOW. THUS EXPECT LOWEST
CONDITIONS ACROSS NORTHWEST IL INCLUDING RFD WHERE SOME IFR
CIGS/VIS ARE POSSIBLE. BUT FOR NOW HAVE OPTED TO STAY LOW MVFR
THERE...WITH HIGHER VIS/CIGS AT DPA/ORD/MDW BUT STILL A PERIOD
OF MVFR WITH GYY POSSIBLY ONLY SEEING FLURRIES. CMS
&&
.MARINE...
408 AM CST
HIGH PRESSURE CENTERED OVER THE UPPER OHIO VALLEY WILL MOVE EAST
TO THE CHESAPEAKE BAY TODAY WHILE A TROUGH OF LOW PRESSURE
GRADUALLY DROPS SOUTHWARD FROM NORTHERN TO CENTRAL LAKE MICHIGAN.
THIS TO MAINTAIN SOUTHWEST WINDS ON THE SOUTHERN PORTION OF LAKE
MI WHILE THE TROF BRINGS A WSHFT TO THE N THRU THE CENTRAL PART OF
THE LAKE DURING THE DAY. WEAK LOW PRES TO MOVE NEWRD TO NORTHERN
IL OVERNIGHT AND ACROSS THE CENTRAL LAKES DURING MONDAY.
BIG STORY IS DEEP LOW PRES/MAJOR STORM TO LIFT FROM THE SOUTHERN
PLAINS TUE EVE...REACHING NORTHERN IL BY WED MORNING...AND
CONTINUING TO DEEPEN AS IT MOVES INTO THE CENTRAL LAKES WED AND ON
TO SOUTHERN QUEBEC BY THU MORNING. AS THE LOW MOVE INTO THE
CENTRAL LAKES LATER WED A VERY TIGHT PRES GRADIENT WILL BE IN
PLACE ACROSS THE LAKE. THIS COMBINED WITH LARGE PRESSURE RISES
AND STRONG DEEP CAA IT LOOKS LIKE A HIGH PROBABILITY OF NW-W WINDS
REACHING GALE FORCE BY WED EVE ACROSS THE SOUTHERN 2/3RDS TO
3/4THS OF THE LAKE...WITH A GOOD CHANCE OF HIGH GALES OR EVEN A PD
OF LOWER END STORM FORCE WINDS AS WED NIGHT PROGRESSES. WINDS WILL
ONLY GRADUALLY DIMINISH THU AS THE LOW MOVES FURTHER AWAY BUT
TIGHT PRESSURE GRADIENT MAINTAINED ACROSS THE LAKES AS THE CENTER
OF A LARGE ANTICYCLONE MOVES E ACROSS THE LWR MS VALLEY TO THE TN
VALLEY. WINDS TO FINALLY DROP BLO GALE FORCE THU NIGHT AS THE
CENTER OF THE HI DRIFTS FURTHER E AND OVER THE APPALACHIANS.
TRS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
