FXUS63 KILX 221126
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
526 AM CST TUE DEC 22 2009

.DISCUSSION...
ISSUED 332 AM CST TUE DEC 22 2009
WEAK PRESSURE PATTERN CONTINUES ACROSS THE MIDWEST THIS
MORNING...WITH A VERY WEAK RIDGE FROM THE UPPER MIDWEST TO THE
SERN CONUS. QUASI ZONAL FLOW ALOFT AS UPPER LOW FINALLY MOVING ON
SHORE IN THE PAC NW AND TROF BEGINNING TO TAKE SHAPE OVER THE PAC
COAST. QUICK WAVE PUSHING ACROSS NRN PORTIONS OF THE CWA BRINGING
SOME ACCUMULATING SNOW NORTH OF 74...BUT OVERALL STRONGEST BANDS
OF SHOWERS LIFTING NE. LINGERING OF THESE SHOWERS IS THE FIRST
TROUBLE FOR THE FORECAST. MODELS ARE MAINTAINING A FAR WARMER
TAKE ON THE SYSTEMS FOR MIDWEEK THROUGH THE HOLIDAY...KEEPING THE
SYSTEM RAIN DOMINATED BEYOND TUE NIGHT WED MORNING. INITIAL COLD
TEMPERATURES WILL RESULT IN A CHANCE OF SOME LIGHT ICE
ACCUMULATION IN THE NORTH...MAKING MANY HOLIDAY SHOPPING/TRAVEL
ISSUES A CONCERN. STRONG SYSTEM PUSHES INTO CENTRAL ILLINOIS
THURSDAY...WITH HEAVY RAIN...STRONG WINDS...AND THE CHANCE FOR
THUNDERSTORMS...FEELING A BIT MORE LIKE A SPRING FORECAST THAN A
DECEMBER ONE. THAT BEING SAID...LIGHT SNOWFALL AND FLURRIES LINGERING
INTO CHRISTMAS MORNING AS THE SYSTEM SLOWS CONSIDERABLY. 

MODELS ARE IN PRETTY DECENT AGREEMENT OVERALL...AND CURRENT
FORECAST HAS VERY LITTLE SHIFT FROM PREVIOUS.

SHORT TERM...TODAY AND TOMORROW...
WAVE PASSING THROUGH TAKING THE MOST EFFICIENT SNOW SHOWERS OUT OF
CWA EARLY THIS MORNING...THOUGH OVERALL EFFECT OF THE WAVE AND
LIFT ACROSS THE REGION IS SCT SHOWERS. WITH PLENTY OF RETURNS
STILL POPPING UP ON RADAR...HAVE EXPANDED A SLIGHT CHANCE OVER
MUCH OF THE CWA FOR THIS MORNING. AND WITH A WEAK BOUNDARY
STARTING TO PUSH UP THRU KS/MO ON SAT IMAGERY AS WE GO THRU A
PATTERN SHIFT...KEEPING THE CHANCES THROUGH THE AFTERNOON. RAMPING
UP THE CHANCES A BIT IN THE OVERNIGHT. FORECAST MODELS BEING
SUBTLE WITH THE CHANCES FOR PRECIP WITH THE LAST RUN...BUT JUST
NOT WILLING TO ABANDON THEM AS A WEAK INVERTED TROF MAINTAINING ON
SFC PATTERN AS THE THERMAL GRADIENT INCREASES WITH SFC LOW
DEVELOPING IN THE SRN PLAINS. LIGHT ICE ACCUMULATION/GLAZING
POSSIBLE NORTH OF INTERSTATE 74 TONIGHT AND INTO TOMORROW MORNING
AS THE PRECIP SPREADS INTO COLD AIR ALREADY IN PLACE. 

SLOWLY WARM AIR PUSHING INTO THE MID LEVELS FIRST ON WED WHILE SFC
FLOW REMAINS EASTERLY...THOUGH IN COMBINATION WITH SOME SIMPLE
DAYTIME WARMING...THE CHANCE FOR FREEZING PRECIP PUSHES NORTHWARD
AND ILX BECOMES DOMINATED BY RAIN. AS THE LOW PUSHES CLOSER...THE
CHANCE FOR THUNDER MOVES INTO THE SOUTHERN CWA. SCT HEAVY RAINFALL
AMOUNTS ARE POSSIBLE AT THIS TIME...BUT THE BEST CHANCES FOR HEAVY
RAIN LIKELY THE NEXT DAY.

LONG TERM...THURSDAY THROUGH SATURDAY...
NOT A LOT OF CHANGE OVERALL...HEAVY RAINS AND WINDY THROUGH
CHRISTMAS EVE...WITH A CHANGE OVER TO SNOW FOR FRI MORNING ON THE
BACKSIDE OF THE SYSTEM AS THE LOW WRAPS UP AND COLD AIR SOAKS IN.
FLURRIES INTO SAT MORNING AS THE LOW SLOWS ON ITS PROGRESSION
THROUGH THE GREAT LAKES. ONE MAJOR THING TO WATCH OUT FOR IN THE
NEXT FEW RUNS OF THE OPERATIONAL MODELS IS THE 06Z NAMS TAKE ON
THE SYSTEM. IT SEEMS TO BE CATCHING ON TO THE BROADER TROF CONCEPT
IN THE MIDDLE OF THE CONUS...AND NOTHING TO PUSH THE UPPER TROF
INTO A NEG TILT. AS A RESULT...THE SFC SYSTEM IS QUITE A BIT
WEAKER WITH FAR LESS EXPLOSIVE DEVELOPMENT. GOOD NEWS...COULD BE
LESS BLUSTERY. BAD NEWS...COULD MEAN REDUCED WAA WHICH MIGHT
CHANGE PRECIP TYPES HERE AND THERE.

HJS

&&

.AVIATION...
ISSUED 526 AM CST TUE DEC 22 2009...FOR THE 12Z TAFS

LIGHT SNOW HAS LIFTED TO THE NE OF THE TAF SITES THIS MORNING.
LIGHT FOG HAS SETTLED INTO THE AREA...WITH MVFR VIS EXPECTED IN
MOST AREAS. SOME FREEZING FOG WILL BE POSSIBLE...MAKING TRAVEL
SURFACES QUITE SLIPPERY EARLY THIS MORNING.

DRIZZLE MAY BEGIN AS EARLY AS 22Z...BUT MOST AREAS SHOULD REMAIN
DRY UNTIL AFTER 00Z. AS TEMPS FALL TONIGHT...FZDZ/FZRA POTENTIAL
WILL INCREASE...ESPECIALLY FOR PIA AND BMI. CMI MAY SEE FZDZ AS
WELL. LIGHT ICING WILL BE POSSIBLE...WITH ICE ACCUMULATION UP TO A
TENTH OF AN INCH. MVFR VIS AND IFR CIGS WILL BE LIKELY OVERNIGHT
AS WELL...WITH A CHANCE OF IFR VIS/LIFR CIGS.

WINDS WILL REMAIN SOUTHEAST OVER THE NEXT 24 HOURS...WITH A FEW
GUSTS NEAR 20KT AT TIMES.

SHIMON
&&

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

$$