FXUS63 KILX 072100
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
300 PM CST MON DEC 7 2009

.DISCUSSION...
ISSUED 300 PM CST MON DEC 7 2009

OBVIOUS FOCUS IS ON THE MAJOR WINTER STORM FOR TUESDAY AND
WEDNESDAY.

GFS/ECMWF CONTINUE TO MATCH QUITE CLOSELY ON TAKING THE SURFACE LOW
ACROSS OUR CWA FROM SW TO NE...ALMOST DIRECTLY OVER PEORIA AROUND
MIDNIGHT TUES NIGHT. THE PROGRESSION OF THE RAIN-SNOW LINE
CONTINUES TO BE THE MOST PROBLEMATIC PART OF THE FORECAST.

THERE IS ENOUGH CONFIDENCE IN THE WARNING LEVEL SNOW TOTALS FOR KNOX
AND STARK THAT WE WILL BE ISSUING A WINTER STORM WARNING FOR
THEM...WHILE ADVISORY LEVEL SNOWS...OR A MIX OF SNOW AND
SLEET...WILL AFFECT THE ROW OF COUNTIES FROM SCHUYLER AND
FULTON...NORTHEAST TO MARSHALL AND WOODFORD.

THE STRONG NATURE OF THE STORM WILL BRING VERY WARM AIR NORTHWARD
AHEAD OF THE LOW...WHICH WILL CHANGE SNOW TO RAIN OVER A MAJORITY
OF OUR COUNTIES...EXCEPT FOR MAYBE KNOX AND STARK. THE TIMING AND
LOCATION OF THAT CHANGE-OVER IS CRITICAL TO SNOW TOTALS.

SHORT TERM...TONIGHT THROUGH WEDNESDAY NIGHT.

WAA FLOWS ALOFT WILL BRING SNOW CHANCES TO OUR FAR WESTERN CWA
ALREADY BY LATE TONIGHT. SOME LIGHT ACCUMULATION MAY OCCUR
NORTHWEST OF THE IL RIVER ON TUESDAY MORNING...BUT STEADIER SNOWS
ARE EXPECTED TUESDAY AFTERNOON. AN INCH OR TWO OF SNOW MAY
ACCUMULATE BY LATE TUESDAY AFTERNOON...BUT THE HEAVIEST SNOWFALLS
ARE EXPECTED TUESDAY EVENING...AS THE LOW APPROACHES WESTERN IL. 

OMEGA FIELDS INDICATE SIGNIFICANT RISING MOTIONS TUESDAY
NIGHT...WHICH COULD SUPPORT SNOWFALL RATES OF 1 TO 2 INCHES AN
HOUR FOR SHORT PERIODS OF TIME. THE POTENTIAL FOR HEAVIEST SNOWS
ACROSS AREAS NW OF THE IL RIVER WILL BE FROM 7 PM TO 3 AM.

AT THE SAME TIME TUESDAY NIGHT...WARM AIR SURGING NORTH AHEAD OF THE
LOW WILL CHANGE ANY SNOW TO RAIN FOR MOST OF THE CWA SOUTHEAST OF
THE IL RIVER. SOME SLEET WILL BE POSSIBLE ALONG THE TRANSITION
ZONE...ALONG WITH PERIODS OF FREEZING RAIN. HOWEVER...ANY GLAZING
WILL LIKELY MELT AS TEMPERATURES CONTINUE TO RISE FROM MIDNIGHT TO
6 AM WEDNESDAY. THE RAIN THAT FALLS WILL WORK TO MELT ANY SNOW
ACCUMULATIONS FROM EARLIER.

BY WEDNESDAY MORNING THE LOW WILL QUICKLY INTO MICHIGAN...AND
NORTHWEST WINDS WILL INCREASE DRAMATICALLY. SOME LIGHT SNOW MAY
CONTINUE ON WEDNESDAY...BUT ACCUMULATIONS WILL BE EXTREMELY
DIFFICULT TO DETERMINE AS SUSTAINED WINDS OF 25 TO 30 MPH...WITH
GUSTS TO 40 MPH...SIGNIFICANTLY BLOW THE SNOWPACK AND FALLING
LIGHT SNOW. TRAVEL WILL BECOME VERY HAZARDOUS AS THE TEMPERATURES
FALL DURING THE AFTERNOON ON WEDNESDAY. WET ROADS WILL RE-FREEZE
IN THE COLD AIR.

WINDS SHOULD DIMINISH WED NIGHT...AS OUR COLDEST AIR OF THE SEASON
SETTLES INTO C IL. ANY AREAS WITH SNOW PACK WILL SEE THE COLDEST
OVERNIGHT LOWS. 

LONG TERM...THURSDAY THROUGH MONDAY.

DRY HIGH PRESSURE SHOULD KEEP THE WEATHER QUIET THROUGH NEXT
WEEKEND. THERE ARE SOME INDICATIONS OF A WEAK SHORTWAVE FOR FRIDAY
OR FRIDAY NIGHT...WITH SOME LIGHT SNOW POSSIBLE. BUT FOR NOW WE
KEPT JUST SLIGHT CHANCES IN THE FORECAST.

SHIMON
&&

.AVIATION...
ISSUED 1122 AM CST MON DEC 7 2009

LOWER CEILINGS WILL BE THE MAIN ISSUE FOR THE FIRST AND LAST
PORTIONS OF THE TAF PERIOD. 

CEILINGS HAVE BEEN CREEPING UPWARD THIS MORNING...AND HAVE MAINLY
REACHED THE 1200 FT RANGE WITH SOME AREAS A FEW HUNDRED FEET
LOWER. VISIBILITIES ALSO SLOWLY INCREASING FROM WEST TO EAST...AS
A WEAK TROUGH PUSHES EAST ACROSS THE TAF SITES. HUMIDITY ANALYSIS
PLOTS FROM THE MODELS SHOWING THE CEILINGS SHOULD SLOWLY INCREASE
INTO THE EVENING...BUT STILL REMAIN IN THE MVFR RANGE AROUND
KPIA/KBMI. 

CEILINGS AND VISIBILITIES EXPECTED TO BEGIN DECREASING AFTER
MIDNIGHT AGAIN...AS THE EFFECTS OF A MAJOR STORM SYSTEM BEGIN TO
IMPACT THE AREA. SHOULD SEE SOME AREAS OF LIGHT SNOW DEVELOPING
ACROSS THE NORTHERN TAF SITES TOWARD DAYBREAK...TRANSITIONING INTO
MORE OF A RAIN/SNOW MIX BY THE END OF THE FORECAST PERIOD. WILL
LEAVE THE REMAINING TAF SITES DRY AT THIS TIME...AS THE
PRECIPITATION WILL BE MORE LIKELY JUST BEYOND THE TAF PERIOD.

GEELHART
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM NOON TUESDAY TO 6 PM CST WEDNESDAY 
FOR ILZ029>031-036-037-040-041.

WINTER STORM WARNING FROM NOON TUESDAY TO 6 PM CST WEDNESDAY FOR 
ILZ027-028.

&&

$$