000 
FXUS63 KILX 260515
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1115 PM CST TUE DEC 25 2007

.DISCUSSION...
ISSUED 830 PM CST TUE DEC 25 2007

WEATHER QUIET TONIGHT AND WILL REMAIN THAT WAY THROUGH MOST OF 
WEDNESDAY. WITH DECREASING WINDS...THE TEMPERATURE RANGE ACROSS THE 
FORECAST AREA IS GETTING PRETTY WIDE AS LOCAL EFFECTS TAKE OVER. 
WILL PROBABLY KNOCK OFF A DEGREE OR TWO FROM MIN TEMPS GRIDS IN THE 
EAST WHERE THE WINDS ARE LIGHTEST. WILL ALSO DECREASE SKY COVER 
EVERYWHERE...WITH ONLY A FEW CIRRUS EXPECTED.

04
&&

.AVIATION...
ISSUED 1115 PM CST TUE DEC 25 2007

LIGHT SOUTHEASTERLY FLOW AND UNLIMITED CEILINGS/VISIBILITIES WILL BE 
THE RULE FOR CENTRAL ILLINOIS THROUGH AT LEAST 18Z WED. AFTER 
THAT...MID AND HIGH LEVEL CLOUDS WILL OVERSPREAD THE AREA FROM WEST 
TO EAST AS THE NEXT WEATHER SYSTEM APPROACHES. UPPER SHORTWAVE AND 
ITS ATTENDING BROAD SURFACE LOW/COLD FRONT WILL PASS THROUGH AFTER 
00Z THU. EXPECT MAINLY RAIN THROUGH 06Z THU AT PIA/SPI/DEC...WITH A 
RAIN/SNOW MIX POSSIBLE AT BMI/CMI.

04
&&

.PREV DISCUSSION...
ISSUED 250 PM CST TUE DEC 25 2007

A PLEASANT...BUT UNCHRISTMASLIKE...DAY IS ONGOING ACROSS CENTRAL AND 
SOUTHEAST ILLINOIS. SOUTHERLY FLOW AHEAD OF AN APPROACHING COLD 
FRONT IN THE UPPER MIDWEST/PLAINS IS TRANSPORTING UNSEASONABLY MILD 
AIR INTO THE AREA WHICH WILL BE WITH US THROUGH WEDNESDAY. THE 
PRECIPITATION CHANCES WITH THE APPROACHING FRONTAL SYSTEM WEDNESDAY 
NIGHT AND WITH OUR NEXT SYSTEM ON THURSDAY NIGHT/FRIDAY ARE THE 
PRIMARY FORECAST CONCERNS TODAY.

12Z MODELS ARE IN REASONABLE AGREEMENT THE NEXT FEW DAYS. SLIGHT 
TIMING DIFFERENCES PERSIST WITH BOTH APPROACHING SYSTEMS IN THE 
SHORT TERM...BUT THESE SHOULD NOT HAVE A SIGNIFICANT IMPACT ON OUR 
SENSIBLE WEATHER.

SHORT TERM...TONIGHT THROUGH FRIDAY...

TONIGHT AND WEDNESDAY...SOUTHERLY LOW LEVEL FLOW WILL KEEP 
UNSEASONABLY MILD CONDITIONS IN PLACE. WENT ABOVE GUIDANCE 
TEMPERATURES GIVEN CURRENT TEMPERATURE/DEW POINTS AND CONTINUED WARM 
ADVECTION. HIGHS TOMORROW WILL LIKELY BE A BIT COOLER DUE TO 
ADDITIONAL CLOUD COVER...BUT STILL QUITE MILD FOR LATE DECEMBER. THE 
SURFACE FRONT WILL REMAIN WEST OF THE FORECAST AREA THROUGH THE DAY 
WEDNESDAY. ISENTROPIC LIFT REMAINS MEAGER/CONDENSATION PRESSURE 
DEFICITS HIGH IN THE WAA PATTERN AHEAD OF THE FRONT...SO HAVE 
REMOVED PRECIPITATION MENTION.

WEDNESDAY NIGHT...COLD FRONT...UPPER JET AND RELATIVELY WELL PHASED 
UPPER WAVE WILL PASS THROUGH THE REGION. THE FORCING WITH THESE 
FEATURES ARE NOT IMPRESSIVE AND MOISTURE IS LIMITED...SO ONLY A 
LIGHT QPF EVENT IS EXPECTED. WARM SURFACE BASED THERMAL PROFILES 
SHOULD KEEP MUCH OF THE PRECIPITATION FALLING AS RAIN...THOUGH IT 
MAY MIX WITH OR CHANGE TO LIGHT SNOW BEFORE ENDING AFTER FROPA. 
LITTLE/NO SNOW ACCUMULATION IS EXPECTED.

THURSDAY...WEAK UPPER/SURFACE RIDGING BUILD WILL BUILD THROUGH THE 
FORECAST AREA. THIS WILL PROVIDE A RETURN TO QUIET WEATHER 
CONDITIONS.

THURSDAY NIGHT AND FRIDAY...A MORE DYNAMIC SYSTEM THAN THE ONE 
COMING THROUGH WEDNESDAY NIGHT WILL LIFT FROM THE SOUTHERN PLAINS 
INTO THE GREAT LAKES BY LATE FRIDAY. THE CURRENT FORECAST 
TRACK...WHICH HAS BEEN FAIRLY STABLE THE PAST SEVERAL MODEL RUNS... 
KEEPS CENTRAL AND SOUTHEAST ILLINOIS MOSTLY ON THE WARM SIDE OF THE 
SYSTEM. STRONG WAA/ISENTROPIC LIFT AND A SURFACE WARM FRONT WILL 
PUSH THROUGH THE FORECAST AREA THURSDAY NIGHT BRINGING A PERIOD OF 
LIGHT RAIN OR SNOW. THE TRAILING COLD FRONT WILL COME THROUGH
FRIDAY...BRINING ANY LINGERING PRECIPITATION TO AN END. THE STORM 
TRACK DOES NOT APPEAR FAVORABLE FOR A SIGNIFICANT PRECIPITATION 
EVENT. THE HEAVIER PRECIPITATION IN THE WAA SIDE OF THE SYSTEM 
SHOULD FALL TO OUR SOUTH/EAST...WHILE THE HEAVIER PRECIPITATION IN 
THE DEFORMATION ZONE SHOULD FALL TO OUR WEST/NORTH. ANY SNOW 
ACCUMULATION WITH THIS SYSTEM WILL BE ON THE LIGHT SIDE DUE TO A 
SURFACE BASED WARM LAYER.

LONG TERM...SATURDAY THROUGH TUESDAY...MODELS/ENSEMBLES LOOKING 
PRETTY SIMILAR TO YESTERDAY AND STILL HAVING THEIR DISAGREEMENTS. 
THERE IS AT LEAST THE POTENTIAL FOR QUIETER WEATHER ACROSS CENTRAL 
AND SOUTHEAST ILLINOIS DURING THE PERIOD. THE GFS HAS BROAD/SHALLOW 
TROFFING OVER THE LOWER 48...WITH MANY WEAK IMPULSES IN THE FLOW. 
THE ECMWF HAS STRONGER/MORE DISTINCT IMPULSES...BUT THE STORM TRACK 
LARGELY STAYS TO OUR SOUTH. THE DGEX/CANADIAN SOLUTIONS ARE 
SOMEWHERE IN THE MIDDLE. IN ANY EVENT...CAN NOT REALLY HANG YOUR HAT 
ON A FAVORED TIME FOR PRECIPITATION ACROSS FORECAST AREA. AS A 
RESULT...HAVE MAINTAINED A SLIGHT CHANCE OF PRECIPITATION FOR PARTS 
OF THE AREA FROM SUNDAY INTO MONDAY WHERE THE GFS SUGGESTS SOME WEAK 
NORTHERN STREAM IMPULSES...BUT WILL LEAVE MENTIONABLE POPS OUT FOR 
NOW.

BAK
&&

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

$$