FXUS63 KILX 080300
AFDILX

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

.DISCUSSION...
ISSUED 847 PM CST MON DEC 7 2009

FORECAST IS PRETTY MUCH ON TRACK TONIGHT AND MAINLY MINOR TWEAKS
TO THE FORECAST ELEMENTS THROUGH DAYBREAK TUE. HAVE 20-40% CHANCE OF
LIGHT SNOW OVERNIGHT ACROSS THE IL RIVER VALLEY WITH BEST CHANCES
IN NW IL BY GALESBURG. LOW OVERCAST SKIES WILL PREVAIL WITH LOWS
IN THE UPPER 20S TO NEAR 30F WITH LIGHT NE WINDS.

MID EVENING SURFACE MAP SHOWS 1033 MB CANADIAN HIGH PRESSURE OVER
SASKETCHEWAN AND MANITOBA AND RIDGING ACROSS IL INTO THE
CAROLINAS. MEANWHILE A 999 MB LOW PRESSURE WAS DEEPENNG OVER SW
CO. MODELS SHOW THIS LOW PRESSURE DEEPENING TO 991 MB TOWARD THE
OK PANHANDLE BY NOON TUE. UPPER LEVEL TROF WAS DIGGING ACROSS THE
WESTERN STATES WITH UPPER LEVEL RIDGE SE OF FL AND IL IN AN
UNSETTLED SW UPPER LEVEL FLOW. INCREASING ISENTROPIC LIFT AHEAD
OF THIS DEEPENING STORM WILL DEVELOP AN AREA OF LIGHT SNOW ACROSS
NW IL DURING OVERNIGHT AND BECOME MORE WIDESPREAD TUE MORNING.
LIGHT SNOW WILL BECOME MIXED WITH SLEET AND POSSIBLY LIGHT
FREEZING RAIN TUE ALONG AND NW OF THE IL RIVER. MEANWHILE RAIN
WILL MOVE NORTHWARD ACROSS SOUTHERN IL TUE MORNING AND INTO
CENTRAL IL ALONG I-72 EARLY TUE AFTERNOON WITH INCREASING MOISTURE
FROM THE SOUTH. HEAVIEST PRECIPITATION STILL APPEARS TO FALL TUE
NIGHT ESPECIALLY TUE EVENING WITH WINTER PRECIP NW OF THE IL RIVER
WHERE WINTER HEADLINES CONTINUE FROM TUE AFTERNOON THROUGH WED.

HUETTL

&&

.AVIATION...
ISSUED 555 PM CST MON DEC 7 2009

MVFR CEILINGS OF 1500 TO 2500 FT WILL PREVAIL THIS EVENING AS MVFR
VISIBILITIES OF 4 TO 6 MILES DEVELOP. CEILINGS WILL LOWER TO 500
TO 1500 FT LATER TONIGHT INTO TUE. EXPECT LIGHT SNOW DEVELOPING AT
PIA AND BMI LATE TONIGHT AND MIXING WITH OR CHANGING TO RAIN LATER
TUE MORNING WITH PIA LAST TO CHANGEOVER TO RAIN DURING MID AFTERNOON
TUE. COULD ALSO BE SOME SLEET ESPECIALLY AT PIA TUE. THINK CHANCES
OF FREEZING RAIN WILL STAY JUST NORTH OF PIA/BMI TUE AS SURFACE
TEMPS CLIMB TO JUST ABOVE FREEZING BY TUE AFTERNOON. LIGHT RAIN
WILL DEVELOP ALONG THE I-72 CORRIDOR DURING EARLY TUE AFTERNOON.
VISIBILITIES WILL LOW TO 1 TO 2 MILES WITH CEILINGS LOWERING
TOWARD 500 FEET DURING TUE. LIGHT WINDS WILL BECOME EAST LATER
TONIGHT AND INCREASE TO 10 TO 15 KTS WITH GUSTS OF 15 TO 20 KTS TUE
AFTERNOON. 

HUETTL

&&

.PREV 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.

&&

.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.

&&

$$