FXUS63 KILX 020506
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1106 PM CST TUE DEC 1 2009

.DISCUSSION...
ISSUED 829 PM CST TUE DEC 1 2009

COLD FRONT ACROSS CENTRAL IA SLOWLY MOVING EAST. THINK THIS COLD
FRONT WL REACH THE WESTERN PART OF THE FORECAST AREA BY AROUND
10Z. CI ARE STREAMING INTO THE STATE AHEAD OF THE LOW PRESSURE
SYSTEM OVER SE TX. WL SEND OUT A FORECAST UPDATE SHORTLY TO
INCREASE CLOUD COVER.

&&

.AVIATION...
ISSUED 1054 PM CST TUE DEC 1 2009

A COLD FRONT OVER EASTERN IA WL MOVE INTO CENTRAL IL WED MORNING.
WINDS WL BEGIN TO SHIFT FROM SOUTH TO NORTH...GENERALLY IN A CCW DIRECTION. AS
THIS FRONT MOVES THROUGH THE TERMINALS. THIS FRONT WL REACH PIA
JUST BEFORE 12Z. A LOW PRESSURE SYSTEM OFF THE LOUISIANA GULF
COAST...WILL TRACK NORTHEAST...INTO THE OHIO RIVER VALLEY WED
AFTERNOON. SCT- BKN DECK OF CI ALREADY STREAMING INTO CENTRAL AND
SOUTHEAST IL AHEAD OF THIS SYSTEM. RAIN AND LOWER CEILINGS WILL
SPREAD INTO AREA FROM SE TO NW...AROUND THE 20Z TO 22Z TIME FRAME.
BEST CHANCES FOR PRECIP ARE IN THE EASTERN TERMINALS. BY THE TIME
PRECIPITATION STARTS AT PIA...ENOUGH COLD AIR SHOULD BE IN
PLACE...SO PRECIPITATION SHOULD BE IN THE FORM OF SN.
PRECIPITATION IN THE REMAINING TERMINAL SITES WL SWITCH TO SN FROM
WEST TO EAST IN THE 01Z TO 04Z TIME FRAME.

DPK
&&

.PREV DISCUSSION...
ISSUED 240 PM CST TUE DEC 1 2009

LATEST SURFACE MAP SHOWING A SURFACE LOW OVER NORTH CENTRAL
MINNESOTA...WITH AN ASSOCIATED COLD FRONT PUSHING SOUTHEAST ACROSS
IOWA. SOUTHERLY FLOW FROM HIGH PRESSURE ACROSS THE MID-ATLANTIC
REGION HAS HELPED PUSH TEMPERATURES INTO THE MID TO UPPER 50S OVER
THE CWA. THIS WILL BE THE LAST TIME IN THE FORESEEABLE FUTURE THAT
SUCH MILD WEATHER WILL BE IN THIS AREA...AS A LOW PRESSURE CENTER
DEVELOPS OVER ONTARIO AND PUSHES WAVES OF COLD AIR INTO THE
MIDWEST LATER THIS WEEK.

MAIN FORECAST ISSUE FOR THIS PACKAGE INVOLVES TIMING OF
PRECIPITATION ON WEDNESDAY...AND ASSOCIATED CHANGEOVER TO SNOW. 

SHORT TERM...TONIGHT THROUGH FRIDAY...

LOW PRESSURE CURRENTLY IN THE NORTHWEST GULF OF MEXICO WILL LIFT
NORTHEAST OVER THE NEXT COUPLE OF DAYS. MODELS ARE IN FAIR AGREEMENT
ON THE EXACT TRACK OF THIS LOW...WITH THE GFS A BIT FURTHER EAST
BY 00Z THURSDAY THAN THE REMAINING MODELS. WILL GO WITH MORE OF A
CONSENSUS FAVORING THE NAM MODEL. 

RAIN SHOULD BEGIN MOVING INTO THE SOUTHEAST CWA BY LATE WEDNESDAY
MORNING...SPREADING NORTH AND WEST TO COVER MOST AREAS EAST OF THE
ILLINOIS RIVER BY LATE AFTERNOON. MAIN ISSUE AT THIS POINT
INVOLVES THE TRANSITION FROM RAIN TO SNOW. BUFKIT SOUNDINGS
INDICATING THE WESTERN CWA SHOULD BEGIN TO SWITCH BY SUNSET...WITH
THE I-55 CORRIDOR CHANGING OVER EARLY IN THE EVENING AND AREAS
EAST OF I-57 HOLDING OFF UNTIL MIDNIGHT OR LATER. HOWEVER...THE
PRECIPITATION SHOULD BE ON THE WANE WHEN THE TRANSITION
OCCURS. BECAUSE OF THIS...AND THE FAIRLY WARM GROUND...AM NOT
LOOKING FOR ANY SIGNIFICANT ACCUMULATIONS...PROBABLY ON THE ORDER
OF A HALF INCH OR LESS. 

BRISK WEST TO NORTHWEST WINDS WILL OCCUR WEDNESDAY NIGHT THROUGH
THURSDAY...WITH A TIGHT PRESSURE GRADIENT OVER THE AREA. A PIECE OF
ENERGY FROM THE ONTARIO UPPER LOW WILL DROP INTO THE UPPER
MIDWEST...AND SWING EASTWARD ACROSS THE REGION THROUGH FRIDAY. ANY
DECENT SNOW CHANCES SHOULD REMAIN TO OUR NORTH...BUT CANNOT RULE
OUT SCATTERED FLURRIES AS THIS FEATURE PASSES. COLDEST WEATHER
DURING THE PERIOD IS EXPECTED ON FRIDAY...WITH AREAS NORTHWEST OF
THE ILLINOIS RIVER LIKELY TO STAY BELOW FREEZING FOR HIGHS.

LONG TERM...SATURDAY THROUGH TUESDAY...

LONGER RANGE MODELS ADVERTISE THE ONTARIO LOW TO FINALLY WEAKEN
AND MOVE EAST AS THE WEEKEND PROGRESSES. QUIET WEATHER IS EXPECTED
MUCH OF THE EXTENDED FORECAST PERIOD...WITH THE MAIN STORM TRACK
REMAINING TO THE SOUTH. TOWARD THE END OF THE PERIOD...THE MODELS
ARE SUGGESTING THE UPPER FLOW BEGINS TO COME OUT OF THE DESERT
SOUTHWEST...AS AN UPPER LOW PUSHES SOUTH THROUGH THE WESTERN
STATES. LATEST ECMWF MODEL QUITE BULLISH IN CRANKING UP A STORM
SYSTEM OVER THE CENTRAL PLAINS...PUSHING NORTHEAST INTO IOWA BY
TUESDAY EVENING...AS IT PUSHES THE UPPER ENERGY EASTWARD AT A
FASTER CLIP. WILL ONLY INCLUDE SILENT 20 POPS AT THIS POINT...DUE
TO NOTICEABLE DIFFERENCES WITH THE GFS AT THIS RANGE.

GEELHART

&&

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

$$