FXUS63 KILX 052325
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
525 PM CST SAT DEC 5 2009

.DISCUSSION...
ISSUED 300 PM CST SAT DEC 5 2009

MAIN CONCERN CONTINUES TO BE THE STORM SYSTEM FOR TUESDAY NIGHT
AND WED MORN. THE 12Z ECMWF/12Z GFS CAME INTO AGREEMENT WITH THE
TRACK OF THE LOW DIRECTLY ACROSS OUR CWA FROM 06Z-12Z WED. THAT
MATCHES RELATIVELY WELL WITH THE CURRENT GRIDS...SO NO MAJOR
CHANGES WERE NEEDED.

SHORT TERM...TONIGHT THROUGH MONDAY.

CLEAR SKIES ARE EXPECTED FOR TONIGHT...AS HIGH PRESSURE SLIDES
AWAY TO THE ESE OF IL. OUR WINDS HAVE ALREADY TURNED AROUND TO THE
SOUTHWEST...WHICH MEANS SOME WARMING ALOFT. THIS MAY HELP KEEP
LOWS UP A FEW DEGREES ABOVE LAST NIGHT...BUT IT WILL STILL BE QUITE
CHILLY. UPSTREAM SFC DEWPOINTS REMAIN IN THE MID TEENS. WINDS
SHOULD DECOUPLE...ALLOWING TEMPS TO DROP QUICKLY AS LONG AS SKIES
REMAIN CLEAR.

WARM FRONTOGENESIS WILL DEVELOP TO THE NW OF IL ON SUNDAY...AS WAA
FLOWS ALOFT BRING CLOUDS INTO OUR CWA DURING THE AFTERNOON. A
SURFACE LOW IS EXPECTED PASS ALONG THE IL RIVER VALLEY LATE SUNDAY
NIGHT AND MONDAY MORNING. A QUICK PUNCH OF DPVA IS EXPECTED IN OUR
AREA SOUTHEAST OF THE LOW DURING THAT TIME. Q-VECTOR CONVERGENCE
AND FAVORABLE JET DYNAMICS POINT TOWARD A QUICK PERIOD OF SNOW
SHOWERS...WITH LESS THAN AN INCH OF ACCUMULATION...MAINLY BETWEEN
MIDNIGHT AND 6 AM. 

A DRY SLOT ALOFT WILL REMOVE OUR ICE CRYSTALS...SETTING THE STAGE
FOR FLURRIES TO CHANGE OVER TO FREEZING DRIZZLE OR DRIZZLE ON
MONDAY MORNING. BRIEF HIGH PRESSURE SHOULD HELP PROVIDE DRY
CONDITIONS MONDAY AFTERNOON AND MONDAY NIGHT.

LONG TERM...TUESDAY THROUGH SATURDAY.

DRY EASTERLY FLOW NEAR THE SURFACE ON TUESDAY MORNING SHOULD HELP
KEEP PRECIPITATION AT BAY UNTIL LATER TUESDAY AFTERNOON AT
LEAST...AND POSSIBLY UNTIL TUESDAY EVENING IN EAST CENTRAL IL. AN
H85 LLJ WILL INCREASE TO AROUND 40KTS BY 00Z WED...ALONG WITH
STRONG ISENTROPIC LIFT. ONCE SATURATION OCCURS IN A DEEP ENOUGH
LAYER ALOFT FOR PRECIP...THE RAIN-SNOW LINE WILL BE THE BIGGEST
CONCERN. 

AT THIS POINT...WITH THE TRACK OF THE LOW EXPECTED TO BE ALMOST
DIRECTLY OVER LINCOLN FROM WSW TO ENE...THE RAIN SNOW LINE MAY
FOLLOW A SIMILAR LINE. SOUTHERLY FLOW AHEAD OF THE LOW MAY KEEP
CMI/BMI IN RAIN CHANCES SLIGHTLY LONGER...WHILE PIA/GBG START AND
REMAIN AS SNOW TUESDAY NIGHT. A BRIEF PERIOD OF SLEET WILL BE
POSSIBLE AT THE ONSET ON TUESDAY EVENING...PRIMARILY FROM SPI TO
LINCOLN TO BMI. IT SHOULD NOT BE A MAJOR PLAYER IN THIS
EVENT...BUT WOULD DEFINITELY ADD TO TRAVEL DIFFICULTIES. 

SNOW TOTALS SHOULD BE HIGHEST FROM GBG TO PIA TO LACON...WHERE 3-5
INCHES OF SNOW WILL BE POSSIBLE. THAT IS WHERE THE DEFORMATION
ZONE WILL RESIDE THE LONGEST. SNOW TOTALS OF 1 TO 3 INCHES MAY
EXTEND AS FAR SOUTH AS SPI/LINCOLN/BMI...DEPENDING ON HOW QUICKLY
THE WARM AIR IS PUSHED TO THE EAST. AREAS SE OF I-72 WILL SEE
MOSTLY RAIN UNTIL LATE TUESDAY NIGHT OR WED MORNING. 

THE SURFACE LOW SHOULD REACH THE IL/IN BORDER BY 12Z WED
MORNING...THEN MOVE OVER LAKE HURON BY 00Z THURS. LINGERING SNOWS
WILL BE MOST PROMINENT NORTH OF A LINE FROM RUSHVILLE TO LINCOLN
TO PARIS...WHERE ANOTHER HALF INCH OR SO COULD ACCUMULATE. OTHER
AREAS WILL MOST LIKELY SEE FLURRIES ON WEDNESDAY. 

WINDS MAY CREATE ADDITIONAL TRAVEL DIFFICULTIES LATE TUESDAY NIGHT
AND WEDNESDAY...AS NW WINDS INCREASE TO 20-30 MPH AT TIMES.
BLOWING AND DRIFTING SNOW MAY REDUCE VISIBILITY FOR MUCH OF THE
MORNING ON WEDNESDAY.

HIGH PRESSURE SHOULD PROVIDE DRY WEATHER FOR THURSDAY. THE NEXT
SYSTEM WILL ARRIVE FRIDAY...WITH SOME LIGHT SNOW POSSIBLE.

&&

.AVIATION...
ISSUED 515 PM CST SAT DEC 5 2009

VFR CONDITIONS ARE EXPECTED THRU THIS FORECAST PERIOD. SATELLITE
DATA INDICATING BAND OF CIRRUS STREAMING EWD OUT OF IOWA INTO
WRN IL EARLY THIS EVENING AND THAT SHOULD BE ABOUT THE EXTENT OF
ANY CLOUD COVER ACRS THE FCST AREA INTO SUNDAY. SURFACE WINDS 
SHOULD REMAIN OUT OF THE SOUTH AT OR BELOW 10 KTS TNT AND 
AT 10 TO 15 KTS ON SUNDAY. 

SMITH
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$