FXUS63 KILX 071144
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
544 AM CST MON DEC 7 2009

.DISCUSSION...
ISSUED 240 AM CST MON DEC 7 2009

PRIMARY FORECAST CHALLENGE CONTINUES TO BE THE TRACK OF THE STORM
SYSTEM ON TUESDAY NIGHT AND WEDNESDAY...AND THE ASSOCIATED PRECIPITATION
TYPE. SURFACE LOW TRACK WILL BE FROM SW TO NE ACROSS THE FORECAST
AREA...WITH MIXED PRECIPITATION NEAR THE LOW TRACK...AND SNOW TO
THE NW OF THE TRACK. AREAS NEAR GALESBURG COULD RECEIVE AROUND 6
INCHES TUES NIGHT AND WED. VERY STRONG NW WINDS WOULD RESULT IN
BLOWING AND DRIFTING SNOW. THEREFORE...WILL EXTEND THE CURRENT
WINTER STORM WATCH THAT BEGINS AT 18Z TUES...TO 00Z THU.

COLD FRONT LOCATED JUST TO THE NORTHWEST OF THE FORECAST AREA
OVERNIGHT. A LOW PRESSURE SYSTEM DEVELOPED IN CENTRAL MO...NOW
RIDING NE ALONG THE FRONT. -SN WAS FALLING TO THE NORTH OF THIS
LOW...WE ARE RECEIVING SNOW ACCUMULATION TOTALS OF AROUND A HALF
INCH AROUND MIDNIGHT.

SHORT TERM...TODAY THROUGH WEDNESDAY

LIGHT SNOW SHOWERS WILL GRADUALLY COME TO AN END WITHIN THE NEXT
FEW HOURS ACROSS THE FORECAST AREA...AS DRIER AIR MOVES IN AT THE
MID LEVELS. ONCE THIS OCCURS...THERE IS VERY LITTLE MOISTURE
AT THE LEVELS BELOW 10C...AND ICE CRYSTALS ARE NO LONGER PRESENT
IN THE CLOUDS. MOSTLY CLOUDY SKIES PERSIST TODAY...AS HIGH CLOUDS
IN ADVANCE OF THE NEXT SYSTEM...STREAM INTO THE FORECAST AREA.

GFS AND ECMWF IN VERY GOOD AGREEMENT ON THE TRACK OF THE SFC LOW
ACROSS IL...ROUGHLY ALONG I-55. THE NAM IS FURTHER TO THE NW...ALONG
THE IL RVR WHICH...IF TRUE...SHIFTS THE HEAVY SNOW JUST NW OF THE
FORECAST AREA. NAM APPEARS TO BE AN OUTLIER...AND THE GFS AND
ECMWF HAVE BEEN FAIRLY SIMILAR TO THE PREVIOUS FORECASTS...SO WL
SIDE WITH THE GFS/ECMWF. 

ISENTROPIC LIFT SETS UP ACROSS THE FORECAST AREA DURING THE DAY
TUES...RESULTING IN PRECIPITATION ACROSS THE AREA. WARM AIR IS
DRAWN INTO THE FORECAST AREA...AND THE PRECIPITATION REMAINS RAIN
ACROSS THE SE PART OF THE AREA. THE AIR IS STILL COLD ENOUGH FOR
SNOW IN THE EXTREME NW. MODEL SOUNDINGS AT 00Z WED IN THE SE SHOW
SOME STEEP MID LEVEL LAPSE RATES...SO THERE MAY BE A FEW THUNDERSTORMS
MIXED IN WITH THE RAIN TO THE SOUTH OF I-70. LOW LEVEL WAA
CONTINUES ACROSS THE CENTRAL PART OF THE FA THROUGH 06Z WED...AND
FORECAST SOUNDINGS ARE INDICATING MIXED PRECIPITATION...AND EVEN
SOME SLEET MIXED IN. MEANWHILE THE SOUNDINGS STILL SUPPORT ALL
SNOW TO THE WEST OF THE IL RIVER. COLD AIR RETURNS EARLY WED
MORNING...AND THE PRECIPITATION IN THE EAST CHANGES TO SNOW. THE
HEAVIEST SNOW ACCUMULATIONS APPEAR TO BE TO THE WEST OF THE IL
RIVER. 

LONG TERM...WEDNESDAY NIGHT THROUGH SATURDAY

SFC LOW MOVES NE OF THE FORECAST AREA WEDNESDAY...VERY STRONG
PRESSURE GRADIENT BEHIND THIS LOW WILL RESULT IN STRONG NW WINDS
WEDNESDAY AND INTO WED NIGHT. THIS WILL RESULT IN BLOWING AND
DRIFTING SNOW...ESPECIALLY WEST OF THE ILLINOIS RIVER...WHERE
SNOWFALL FROM THE TUE NIGHT AND WED SYSTEM IS THE GREATEST. HIGH
PRESSURE BUILDS IN THU MORNING...ALLOWING WINDS TO DIMINISH. VERY
VERY COLD AIR WILL POUR INTO THE FORECAST AREA WEDNESDAY NIGHT
INTO THURSDAY. TEMPERATURES WILL BE A FEW DEGREES COLDER IN AREAS
WHERE SNOWPACK EXISTS...THEREFORE LOWERED TEMPERATURES WED NIGHT
THROUGH THU NIGHT WEST OF THE IL RVR. 

DPK
&&

.AVIATION...
ISSUED 544 AM CST MON DEC 7 2009

IFR AND MVFR CONDITIONS WILL PREVAIL AT ALL SITES THROUGH THE NEXT
24HRS. CIGS BELOW 1KFT WILL BE THE ISSUE FOR THE MORNING FOR BMI
AND PIA...BUT MODELS INDICATE POTENTIAL FOR CIGS TO RAISE TO ABOVE
1KFT FOR THE AFTERNOON. SPI...DEC AND CMI CIGS SHOULD BE JUST
ABOVE 2KFT BUT DEC WILL HAVE CIGS BELOW 1KFT FOR SEVERAL HOURS
THIS MORNING. VIS WILL ALSO BE MVFR CAT FOR ALL SITES THIS MORNING
BUT SHOULD IMPROVE AROUND NOON. WINDS WILL BECOME SOUTHWESTERLY
THIS MORNING BUT THEN BECOME NORTHWESTERLY THIS AFTERNOON AS THE
WEAK LOW PRESSURE AREA MOVES NORTHEAST. 

AUTEN
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH WEDNESDAY 
AFTERNOON FOR ILZ027>030-036-040.

&&

$$