000 
FXUS63 KILX 060521
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1121 PM CST SAT DEC 5 2009

.DISCUSSION...
ISSUED 830 PM CST SAT DEC 5 2009

LATEST SURFACE ANALYSIS INDICATING HIGH PRESSURE TO OUR
EAST...WHILE A STATIONARY FRONTAL BOUNDARY WAS LOCATED ACRS
WRN IOWA. SOUTHERLY GRADIENT BETWEEN THE HIGH TO OUR EAST AND
THE FRONT TO OUR WEST WILL CONTINUE OVERNIGHT...AND THAT COUPLED
WTIH AN INCREASE IN HIGH LEVEL MOISTURE SHOULD KEEP OVERNIGHT
LOWS FROM GETTING AS COLD AS LAST NIGHT. MAY SEE SOME ISOLD
SITES DROP INTO THE UPPER TEENS...BUT THE BULK OF OUR AREA
SHOULD SEE OVERNIGHT LOWS ARND 20. QUITE A BIT OF HIGH LEVEL
CLOUDINESS AROUND ON SUNDAY BUT THAT SHOULDNT PREVENT AFTN
HIGHS FROM WARMING INTO THE UPPER 30S TO LOWER 40S. 

OTHER THAN SOME MINOR ADJUSTMENTS TO THE HOURLY TEMP GRIDS
THIS EVENING...THE CURRENT ZONES ARE IN GOOD SHAPE...AS A 
RESULT...NO UPDATE WILL BE REQUIRED. 

&&

.AVIATION...
ISSUED 1115 PM CST SAT DEC 5 2009

LITTLE CHANGE FROM PREVIOUS DISCUSSION. VFR CONDITIONS ARE
EXPECTED THRU THIS FCST PERIOD. THICKENING CIRRUS SHIELD WL
CONTINUE TO SPREAD NE ACRS CNTRL IL INTO SUNDAY. SOUTHERLY
WINDS WILL PREVAIL INTO SUNDAY MORNING AT SPEEDS OF ARND 10
KTS...WITH WINDS BACKING MORE INTO THE SE BY EVENING. FORECAST
SOUNDINGS SUGGEST SOME MID LEVEL MOISTURE WL INCREASE ACRS THE
AREA BY LATE AFTN AND EVENING SO WL INCLUDE A CIG AOA 10000 FEET
AFTR 19Z...WITH A GRADUAL LOWERING OF CIGS SUNDAY EVENING AS A
WEAK WEATHER DISTURBANCE APPRCHS FROM THE CENTRAL PLAINS. WE MAY
SEE SOME MVFR/IFR CIGS DEVELOP AFTR THIS FCST PERIOD AS THE WEAK
STORM SYSTEM MOVES THRU MONDAY MORNING WITH THE PSBLTY OF SOME
LIGHT SNOW LATE TMRW NIGHT OR MONDAY MRNG.  

SMITH
&&


.PREV DISCUSSION...
ISSUED 300 PM CST SAT DEC 5 2009

MAIN CONCERN CONTINUES TO BE THE STORM SYSTEM FOR TUESDAY NIGHT
AND WED MORN. THE 12Z ECMWF/12Z GFS CAME INTO AGREEMENT WITH THE
TRACK OF THE LOW DIRECTLY ACROSS OUR CWA FROM 06Z-12Z WED. THAT
MATCHES RELATIVELY WELL WITH THE CURRENT GRIDS...SO NO MAJOR
CHANGES WERE NEEDED.

SHORT TERM...TONIGHT THROUGH MONDAY.

CLEAR SKIES ARE EXPECTED FOR TONIGHT...AS HIGH PRESSURE SLIDES
AWAY TO THE ESE OF IL. OUR WINDS HAVE ALREADY TURNED AROUND TO THE
SOUTHWEST...WHICH MEANS SOME WARMING ALOFT. THIS MAY HELP KEEP
LOWS UP A FEW DEGREES ABOVE LAST NIGHT...BUT IT WILL STILL BE QUITE
CHILLY. UPSTREAM SFC DEWPOINTS REMAIN IN THE MID TEENS. WINDS
SHOULD DECOUPLE...ALLOWING TEMPS TO DROP QUICKLY AS LONG AS SKIES
REMAIN CLEAR.

WARM FRONTOGENESIS WILL DEVELOP TO THE NW OF IL ON SUNDAY...AS WAA
FLOWS ALOFT BRING CLOUDS INTO OUR CWA DURING THE AFTERNOON. A
SURFACE LOW IS EXPECTED PASS ALONG THE IL RIVER VALLEY LATE SUNDAY
NIGHT AND MONDAY MORNING. A QUICK PUNCH OF DPVA IS EXPECTED IN OUR
AREA SOUTHEAST OF THE LOW DURING THAT TIME. Q-VECTOR CONVERGENCE
AND FAVORABLE JET DYNAMICS POINT TOWARD A QUICK PERIOD OF SNOW
SHOWERS...WITH LESS THAN AN INCH OF ACCUMULATION...MAINLY BETWEEN
MIDNIGHT AND 6 AM. 

A DRY SLOT ALOFT WILL REMOVE OUR ICE CRYSTALS...SETTING THE STAGE
FOR FLURRIES TO CHANGE OVER TO FREEZING DRIZZLE OR DRIZZLE ON
MONDAY MORNING. BRIEF HIGH PRESSURE SHOULD HELP PROVIDE DRY
CONDITIONS MONDAY AFTERNOON AND MONDAY NIGHT.

LONG TERM...TUESDAY THROUGH SATURDAY.

DRY EASTERLY FLOW NEAR THE SURFACE ON TUESDAY MORNING SHOULD HELP
KEEP PRECIPITATION AT BAY UNTIL LATER TUESDAY AFTERNOON AT
LEAST...AND POSSIBLY UNTIL TUESDAY EVENING IN EAST CENTRAL IL. AN
H85 LLJ WILL INCREASE TO AROUND 40KTS BY 00Z WED...ALONG WITH
STRONG ISENTROPIC LIFT. ONCE SATURATION OCCURS IN A DEEP ENOUGH
LAYER ALOFT FOR PRECIP...THE RAIN-SNOW LINE WILL BE THE BIGGEST
CONCERN. 

AT THIS POINT...WITH THE TRACK OF THE LOW EXPECTED TO BE ALMOST
DIRECTLY OVER LINCOLN FROM WSW TO ENE...THE RAIN SNOW LINE MAY
FOLLOW A SIMILAR LINE. SOUTHERLY FLOW AHEAD OF THE LOW MAY KEEP
CMI/BMI IN RAIN CHANCES SLIGHTLY LONGER...WHILE PIA/GBG START AND
REMAIN AS SNOW TUESDAY NIGHT. A BRIEF PERIOD OF SLEET WILL BE
POSSIBLE AT THE ONSET ON TUESDAY EVENING...PRIMARILY FROM SPI TO
LINCOLN TO BMI. IT SHOULD NOT BE A MAJOR PLAYER IN THIS
EVENT...BUT WOULD DEFINITELY ADD TO TRAVEL DIFFICULTIES. 

SNOW TOTALS SHOULD BE HIGHEST FROM GBG TO PIA TO LACON...WHERE 3-5
INCHES OF SNOW WILL BE POSSIBLE. THAT IS WHERE THE DEFORMATION
ZONE WILL RESIDE THE LONGEST. SNOW TOTALS OF 1 TO 3 INCHES MAY
EXTEND AS FAR SOUTH AS SPI/LINCOLN/BMI...DEPENDING ON HOW QUICKLY
THE WARM AIR IS PUSHED TO THE EAST. AREAS SE OF I-72 WILL SEE
MOSTLY RAIN UNTIL LATE TUESDAY NIGHT OR WED MORNING. 

THE SURFACE LOW SHOULD REACH THE IL/IN BORDER BY 12Z WED
MORNING...THEN MOVE OVER LAKE HURON BY 00Z THURS. LINGERING SNOWS
WILL BE MOST PROMINENT NORTH OF A LINE FROM RUSHVILLE TO LINCOLN
TO PARIS...WHERE ANOTHER HALF INCH OR SO COULD ACCUMULATE. OTHER
AREAS WILL MOST LIKELY SEE FLURRIES ON WEDNESDAY. 

WINDS MAY CREATE ADDITIONAL TRAVEL DIFFICULTIES LATE TUESDAY NIGHT
AND WEDNESDAY...AS NW WINDS INCREASE TO 20-30 MPH AT TIMES.
BLOWING AND DRIFTING SNOW MAY REDUCE VISIBILITY FOR MUCH OF THE
MORNING ON WEDNESDAY.

HIGH PRESSURE SHOULD PROVIDE DRY WEATHER FOR THURSDAY. THE NEXT
SYSTEM WILL ARRIVE FRIDAY...WITH SOME LIGHT SNOW POSSIBLE.


&&

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

$$