FXUS63 KILX 070549
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1149 PM CST SUN DEC 6 2009

.DISCUSSION...
ISSUED 900 PM CST SUN DEC 6 2009

UPDATED THE FORECAST FOR INCREASING LIGHT SNOW CHANCES OVERNIGHT
AND ADDED CHANCE OF FREEZING DRIZZLE TOO SW OF A SPRINGFIELD TO
LAWRENCEVILLE LATE TONIGHT. STILL LOOKS LIKE AROUND A HALF INCH OR
LESS FOR MOST OF CENTRAL IL WITH VERY LITTLE IN SE IL AND HALF TO
1 INCH NW OF THE IL RIVER. ALSO LOWERED LOWS IN THE LOWER 20S
AROUND CHAMPAIGN WHERE TEMPERATURE WAS 22F AT 8 PM AND PROBABLY
NEAR THE LOW AS MID LEVEL CLOUDS BLANKETING THEM BY MID EVENING.

MID EVENING SURFACE MAP SHOWS WEAK 1016 MB LOW PRESSURE NEAR KANSAS
CITY ALONG THE MO/KS BORDER WITH A FRONTAL BOUNDARY EXTENDING
ALONG THE IA/IL BORDER INTO NW MO AND CENTRAL OK. MID LEVEL SHORT
WAVE WAS FROM SW IA INTO EASTERN KS. AREA OF LIGHT SNOW ALONG AND
AHEAD OF THIS FEATURE OVER CENTRAL/SW IA INTO NW MO AND EASTERN
KS/NE. LIGHT SNOW AS FAR EAST AS KIRKSVILLE MO AND OTTUMA IA AND
MOVING ENE.

SHORT RANGE MODELS EJECT SHORT WAVE INTO WEST CENTRAL IL BY DAWN
MON WITH WEAK LOW PRESSURE AND FRONT MOVING INTO NW/WEST CENTRAL IL.
INCREASING ISENTROPIC LIFT TO DEVELOP LIKELY CHANCE OF LIGHT SNOW
DURING OVERNIGHT FROM WEST TO EAST AND THEN DIMINISH DURING MON 
MORNING. WEAK SYSTEM AND LACKING MOISTURE SO SNOW ACCUMULATIONS
SHOULD STAY LIGHT...LESS THAN AN INCH. ADDED CHANCE OF LIGHT
FREEZING DRIZZLE TOO SW OF A SPRINGFIELD TO LAWRENCEVILLE LINE PER
THERMAL PROFILES. LOWS IN THE MID TO UPPER 20S EXCEPT LOWER 20S BY
CHAMPAIGN. TEMPS CURRENTLY NOT TOO FAR FROM THESE LOWS AS BLANKET
OF LOWERING CLOUD COVER AND SSE WINDS 5 TO 10 MPH TO KEEP TEMPS
FROM SLIPPING TOO MUCH MORE OVERNIGHT. 

&&

.AVIATION...
ISSUED 1135 PM CST SUN DEC 6 2009

LIGHT SNOW THAT MOVED INTO SPI JUST AFTER 05Z WITH VISIBILITY DOWN
TO 1 TO 2 MILES AND CEILING DOWN TO 700 FEET WILL SPREAD OVER PIA
AND DEC SHORTLY AND TO BMI AND CMI AROUND 07Z/1 AM AND CMI AROUND
08Z/2 AM. LIGHT SNOW MOVING IN A FEW HOURS QUICKER THAN EARLIER
THOUGH AND VISIBILITIES AND CEILINGS ALSO GETTING DOWN TO IFR
INSTEAD OF MVFR. A HALF INCH OF SNOW REPORTED AT JACKSONVILLE PAST
2 HOURS. BETWEEN HALF AND 1 INCH OF SNOW EXPECTED ACROSS CENTRAL
IL OVERNIGHT WHICH WILL STICK ON UNTREATED ROADWAYS WITH SURFACE
AND GROUND TEMPS STAYING NEAR OR JUST BELOW FREEZING. THINK MIX OF
SLEET AND LIGHT FREEZING DRIZZLE WILL STAY JUST SW OF SPI
OVERNIGHT INTO MON MORNING WILL WILL BE CLOSE TO SPI. LIGHT SNOW
TO DIMININSH DURING MID MORNING MON AS SHORT WAVE OVER CENTRAL MO
LIFTS INTO NE IL BY 15Z/9 AM MON AND THEN INTO THE GREAT LAKES
MON. MODELS ELEVATE CEILINGS TO VFR MON AFTERNOON/EVENING BUT KEEP
BROKEN TO OVERCAST CEILINGS OF 3-5K FT. WEAK 1017 MB LOW PRESSURE
OVER WEST CENTRAL MO WITH A FRONTAL BOUNDARY EXTENDING TO ALONG
THE IL/IA BORDER. SSE WINDS 7 TO 11 KTS TO TURN WNW AFTER FRONT
PASSES EAST ACROSS IL DURING BY WED AFTERNOON...THEN BE LIGHT AND
VARIABLE OR LIGHT NNE MON EVENING.

HUETTL

&&

.PREV DISCUSSION...
ISSUED 300 PM CST SUN DEC 6 2009

THE FIRST BIG WINTER STORM OF THE SEASON IS STILL INDICATED FOR
TUESDAY AFTERNOON THROUGH WEDNESDAY MORNING. THE ALL-IMPORTANT SURFACE
LOW TRACK IS STILL EXPECTED TO PASS DIRECTLY ACROSS OUR CWA FROM
SW TO NE. WE WILL HAVE THE TRANSITION ZONE TO DEAL
WITH...ESPECIALLY TUESDAY NIGHT WHEN WE EXPECT THE LOW NEARLY
OVERHEAD BETWEEN 06Z-12Z. THE RAIN-SNOW LINE MAY BE ACCOMPANIED
BY SLEET OR BRIEF FREEZING RAIN LATE TUESDAY AFTERNOON AND TUESDAY
NIGHT. INITIAL THOUGHTS THIS MORNING WERE THAT WE WOULD MOST
LIKELY ONLY SEE ADVISORY LEVELS OF SNOW IN OUR NW ZONES.

HOWEVER...DUE TO THIS BEING THE FIRST BIG STORM THIS YEAR...THE
POTENTIAL FOR WARNING LEVEL SNOWS WITH MAJOR TRAVEL IMPACT...WE
DECIDED TO GO WITH A WINTER STORM WATCH FOR AREAS NORTHWEST OF THE
ILLINOIS RIVER. THE WATCH WILL BEGIN AT NOON TUESDAY THROUGH NOON
WEDNESDAY.

STRONG WINDS ON WEDNESDAY WILL LIKELY CAUSE BLOWING AND DRIFTING
SNOWS...WHICH WILL COMPLICATE TRAVEL CONDITIONS.

SHORT TERM...TONIGHT THROUGH WEDNESDAY.

VIRGA IS ALREADY SHOWING UP ON RADAR ACROSS IOWA/MISSOURI...AS WAA
FLOWS ALOFT BEGIN TO INCREASE MOISTURE AND LIFT OVER OUR AREA.
ISENTROPIC ANALYSIS SHOWS THE BEST CHANCES FOR FOCUSED LIFT WILL
BE 06Z TO 12Z TONIGHT...WHEN WE EXPECT A QUICK PUNCH OF DPVA FROM
A VIGOROUS MID LEVEL VORT MAX. WE KEPT LIKELY POPS AFTER
MIDNIGHT...WHERE WE COULD SEE A DUSTING TO A HALF INCH IN OUR
EASTERN CWA...WITH UP TO AN INCH IN THE WEST...CLOSER TO THE TRACK
OF THE SURFACE LOW. 

MONDAY MORNING...THE DRY AIR ALOFT WILL REMOVE ICE CRYSTALS FROM
THE MID LEVELS...CAUSING ANY LINGERING FLURRIES TO CHANGE TO
FREEZING DRIZZLE FROM SW TO NE. 

A BRIEF BREAK IN THE ACTION IS EXPECTED FOR MONDAY NIGHT...AS THE
MAJOR STORM SYSTEM TAKES SHAPE IN THE PLAINS. BY TUESDAY
MORNING...WE WILL MOST LIKELY SEE WAA SNOWS APPROACHING OUR
WESTERN CWA. DRY EASTERLY FLOW AT THE SURFACE SHOULD KEEP
MEASURABLE SNOWS AT BAY UNTIL TUESDAY AFTERNOON...WHEN THE
STRENGTH OF THE OMEGA WILL ALLOW PRECIP TO OVERCOME THE DRY LOWER
LAYERS.

AS MENTIONED EARLIER...WE STARTED OUR WINTER STORM WATCH AT NOON
ON TUESDAY...AS SNOW ACCUMULATION MAY BEGIN NEAR GALESBURG AROUND
THEN. A 40-50 KT LOW LEVEL JET WILL ENHANCE THE WAA SNOWS IN OUR
NW ZONES. AREAS SOUTHEAST OF THE IL RIVER MAY SEE A BRIEF PERIOD
OF SNOW OR SLEET AT THE ONSET OF PRECIPITATION LATE TUESDAY
AFTERNOON AND EARLY TUESDAY EVENING...BEFORE CHANGING OVER TO
RAIN. AREAS ALONG THE IL RIVER MAY SEE AN MORE EXTENDED PERIOD OF
SLEET POTENTIAL THROUGH TUES EVENING...BEFORE THE RAIN-SNOW LINE
BECOMES ESTABLISH NEAR THE TRACK OF THE SURFACE LOW. 

WE WILL LIKELY SEE A VERY SHARP CUTOFF BETWEEN HEAVY SNOW AND
LITTLE TO NO SNOW SOMEWHERE IN OUR NW CWA. THAT IS THE MAJOR
CHALLENGE OF THIS WINTER EVENT. IF THE LOW TRACKS ANY FARTHER TO
THE NW...WE COULD SEE MUCH LESS SNOW IN OUR WATCH AREA. IF IT
TRACKS FARTHER SE...THE HEAVY SNOW WILL EXPAND TO THE SE TOWARD
LINCOLN AND BMI AS WELL. AFTER COORDINATION WITH SURROUNDING
OFFICES...WE DECIDED TO LEAN TWRD CAUTION...AND ISSUE THE WATCH NW
OF THE IL RIVER FROM NOON TUES THROUGH NOON WEDNESDAY.

AT 12Z WED...THE SURFACE LOW IS EXPECTED TO NE NEAR JUST SOUTH OF
CHICAGO ALONG THE IL/IN BORDER. THE GFS AND ECMWF ARE IN RELATIVE
AGREEMENT WITH THAT LOCATION...WHILE THE NAM IS FARTHER NW AND THE
CANADIAN GLOBAL IS FARTHER EAST. 

REGARDLESS...WNW WINDS BEHIND THE LOW WILL INCREASE DRAMATICALLY
BY NOON WED...WITH BLOWING AND DRIFTING SNOW LIKELY IN OUR N CWA.

SNOW TOTALS IN THE WATCH AREA MAY REACH UP TO 6
INCHES...ESPECIALLY THE CLOSER TO GALESBURG YOU GET. THE AREAS
CLOSER TO THE IL RIVER MAY BE MORE IN THE 3-5 INCH RANGE...DEPENDING
ON THE RAIN SNOW LINE...BUT ENOUGH OF EACH COUNTY COULD SEE 6 INCH
TOTALS...SO WE INCLUDED THE SCHUYLER TO MARSHALL ROW OF COUNTIES.

ISENTROPIC DOWNGLIDE AND A DRY PUNCH OF AIR ALOFT SHOULD HELP SHUT
DOWN FALLING SNOW WEDNESDAY AFTERNOON. HOWEVER...STRONG WNW WINDS
AROUND 30 MPH WILL KEEP BLOWING AND DRIFTING SNOW GOING FOR AREAS
THAT RECEIVE MEASURABLE SNOWS.

LONG TERM...THURSDAY THROUGH SUNDAY.

LITTLE IN THE WAY OF PRECIPITATION IS INDICATED FOR LATE NEXT WEEK
AND WEEKEND...AS HIGH PRESSURE KEEPS WEAK SHORTWAVES JUST TO THE
NORTH AND SOUTH OF OUR AREA. TEMPERATURES WILL REMAIN ON THE
CHILLY SIDE...AS WE CONTINUE TO BE UNDER THE INFLUENCE OF CANADIAN
AIR.

&&

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

&&

$$