Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 271856
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
156 PM CDT MON OCT 27 2008

.DISCUSSION...
ISSUED 145 PM CDT MON OCT 27 2008

UPPER TROF FIRMLY ENTRENCHED OVER THE GREAT LAKES THIS AFTERNOON
BRINGING CHILLY TEMPERATURES TO THE REGION. SEVERAL WEAK DISTURBANCES
ROTATING SOUTHEAST OUT OF THE NRN PLAINS COMBINED WITH SOME DAYTIME
HEATING HAS PRODUCED SOME ISOLATED SPRINKLES ACRS PARTS OF EAST
CENTRAL AND SOUTHEAST ILLINOIS OVR THE PAST SVL HOURS. SURFACE HIGH
PRESSURE TO OUR WEST WILL GRDLY WORK ITS WAY EAST OVR THE NEXT SVL
DAYS BRINGING UNSEASONABLY COLD TEMPERATURES TO THE AREA THRU WED.
UPPER TROF TO SHIFT OFF TO THE EAST AFTR WED ALLOWING THE CENTER OF
THE COLD AIR MASS TO SHIFT AWAY FROM CNTRL IL BRINGING MODERATING
TEMPERATURES TO THE AREA FOR THE END OF THE WEEK.

SHORT TERM...TONIGHT THROUGH THURSDAY
MAIN FORECAST CONCERN WL BE WITH THE POTENTIAL FOR A WIDESPREAD
FREEZING TONIGHT AS ALL MODELS INDICATE THE CU/STRATOCU CLOUD FIELD
WL DISSIPATE WITH THE LOSS OF DAYTIME HEATING LATE THIS AFTN WITH
CLEARING SKIES FROM WEST TO EAST OVERNIGHT. WESTERN EDGE OF CLOUD
SHIELD LOOKING MORE CELLULAR AS WE HEAD THRU THE EARLY AFTERNOON
HOURS AS CONVECTIVE TEMPS HAVE BEEN REACHED...SUGGESTING ONCE WE
LOSE THE DAYTIME HEATING...WE SHOULD SEE A DIMINISHING OF THE
CLOUD COVER LATER THIS EVENING. 12Z MAV GUID ONCE AGAIN HAS WARMED
TEMPS UP A FEW DEGREES (2 TO 4 DEGREES) FROM THE 00Z RUN FOR THE
OVERNIGHT LOWS INDICATING THAT CLOUDS MAY BE SLOWER TO CLEAR THAN
EXPECTED. STILL NOT MAKING ANY SIGNIFICANT CHANGES TO GOING TEMPS
BASED ON THE ABOVE REASONING. IN ADDITION...UPSTREAM OBS SHOWING
DEW POINTS HAVE MIXED DOWN INTO THE UPPER TEENS TO LOWER 20S...SO
ANY SIGNIFICANT BREAKS IN THE CLOUD COVER LATER TONIGHT WL LEAD
TO OVERNIGHT LOWS AS COLD AS THE MET/FWC GUIDANCE VALUES (MID TO
UPPER 20S). CURRENT HEADLINES FOR FREEZING TEMPERATURES STILL
LOOKING ON TARGET FOR TUESDAY MORNING.

THE LARGE COLD FAIR WEATHER SYSTEM WILL EDGE SLOWLY EASTWARD ON
TUESDAY AND WEDNESDAY CONTINUING TO BRING RATHER CHILLY TEMPERATURES
TO CENTRAL ILLINOIS. 850 TEMP FORECASTS INDICATE HIGH TEMPS IN THE
UPPER 40S ON TUESDAY WITH MID OR UPPER 50S LOOKING REASONABLE FOR
WED AFTN. ANOTHER COLD NIGHT LOOKS LIKELY TUESDAY NIGHT INTO WED
MRNG WITH READINGS AT OR BELOW GUID VALUES...IN THE 25 TO 30
DEGREE RANGE. THE ACTUAL SFC RIDGE AXIS DOES NOT SHIFT EAST OF OUR
AREA UNTIL WEDNESDAY NIGHT WHICH WILL ALLOW A WEAK SOUTHERLY
RETURN FLOW TO DEVELOP ACRS THE AREA BY THEN. INCREASING SOUTHERLY
FLOW ON THURSDAY SHOULD SET THE STAGE FOR A NICE WARMUP ACRS THE
MIDWEST WITH AFTN READINGS IN THE MID OR UPPER 60S.

LONG TERM...FRIDAY THROUGH MONDAY
MEDIUM AND LONGER RANGE MODELS IN GOOD OVERALL AGREEMENT WITH THE
PATTERN OVER THE LOWER 48. THE DEEP TROF OVER THE LAKES SHIFTS
EAST OF THE AREA AFTER WEDNESDAY WITH OUR FLOW BECOMING MORE ZONAL
BY THE END OF THE WEEK. A WEAK SHORTWAVE CONTINUES TO PUSH ACRS
THE REGION LATE THU INTO EARLY FRIDAY BUT WITH NO APPARENT WX ACRS
OUR AREA. A MORE SIGNIFICANT SHORTWAVE WILL PROGRESS ACRS THE NRN
PLAINS AND UPPER LAKES LATER ON FRIDAY WHICH WILL HELP TO DRAG A
WEAK COLD FRONT ACRS THE AREA. MODELS CONTINUE TO SUGGEST ANY
PRECIP ASSOCIATED WITH THE UPPER WAVE AND FRONTAL BOUNDARY WILL
REMAIN TO THE NORTH OF THE AREA. ANOTHER FAIRLY LARGE COOL HIGH
PRESSURE SYSTEM WILL AFFECT THE AREA FOR THE START OF THE WEEKEND.
HOWEVER...WITH THE HIGH FORECAST TO DRIFT EAST ACRS THE UPPER
LAKES RATHER THE SOUTHEAST INTO OUR AREA...IT APPEARS THE COLDEST
TEMPERATURES WL REMAIN TO OUR NORTH OVR THE WEEKEND. 850 TEMPS DO
COOL OFF SOME 3 TO 6 DEGREES C SUGGESTING AFTN HIGHS ON SATURDAY
WILL DROP BACK INTO THE UPPER 50S NORTH TO THE MIDDLE 60S SOUTH.

WITH UPPER TROFS LOCATED OFF THE EAST AND WEST COASTS AND RIDGING
OVR THE CENTER OF THE COUNTRY SUNDAY AND MONDAY...IT LOOKS AS
THOUGH TEMPS WILL BE AVERAGING OUT ABOVE NORMAL STARTING SUNDAY
AFTN AND CARRYING INTO EARLY NEXT WEEK. THE NEXT CHANCE FOR ANY
SIGNIFICANT PRECIP APPEARS TO BE HOLDING OFF UNTIL AFTER THIS
FORECAST PERIOD.

SMITH
&&

.AVIATION...
ISSUED 1240 PM CDT MON OCT 27 2008

VFR CONDITIONS SHOULD PREVAIL ACROSS THE CENTRAL ILLINOIS TEMINALS
THROUGH 18Z/TUE. VERY STRONG UPPER LEVEL TROF FROM HUDSON BAY
SOUTHWARD ACROSS THE GREAT LAKES INTO THE OH/TN VALLEYS WILL SHIFT
EASTWARD INTO THE ATLANTIC STATES TUE. A SHORT WAVE OVER CENTRAL
WI WILL DIVE SSE ACROSS NE/EAST CENTRAL IL THIS AFTERNOON BRINGING
A FEW LIGHT SHOWERS TO MAINLY NE IL. DID NOT ADD SHOWERS TO
CENTRAL IL TAF SITES THINKING JUST SPRINKLES WITH VSBYS STAYING
ABOVE 5 MILES AND BEST CHANCE ALONG I-74. BROKEN TO OVERCAST
STRATOCUMULUS CLOUDS OF 4 TO 6K FT AND AS LOW AS 3 TO 4K FT AT CMI
AND BMI THIS AFTERNOON TO CLEAR FROM NW TO SE DURING THIS EVENING
WITH CLEAR SKIES OVERNIGHT. BREEZY NW WINDS 12 TO 17 KTS AND GUSTS
OF 22 TO 28 KTS TO DIMINISH TO AROUND 10 KTS DURING THIS EVENING.
STRONG ELONGATED HIGH PRESSURE FROM NORTH TX INTO THE WESTERN
DAKOTAS TO BUILD EASTWARD TO ALONG THE TX/LA BORDER NORTHWARD ACROSS
MO/IA/MN BY TUE AFTERNOON. THIS TO BRING MOSTLY SUNNY SKIES TO
CENTRAL IL TUE WITH SCATTERED CU/STRATO CU CLOUDS AFTER 15Z/TUE
WITH NW WINDS 10 TO 15 KTS.

HUETTL
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
FREEZE WARNING FROM 1 AM TO 9 AM CDT TUESDAY FOR ILZ027>031-
036>038-040>057-061>063-066>068-071>073.

&&

$$




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