Issued by NWS Central Illinois
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000 FXUS63 KILX 271634 AFDILX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LINCOLN IL 1134 AM CDT MON OCT 27 2008 .DISCUSSION... ISSUED 1130 AM CDT MON OCT 27 2008 FORECAST IN GOOD SHAPE TODAY AND ONLY MINOR TWEAKS TO INCREASE THE NW WINDS AND HIGHS SLIGHTLY IN A FEW SPOTS. MOSTLY CLOUDY...VERY BREEZY AND COOL TODAY WITH A CHANCE OF SPRINKLES AND FLURRIES. HIGHS ONLY IN THE MIDDLE TO UPPER 40S. MUCH COOLER THAN NORMAL HIGHS FOR LATE OCT IN THE UPPER 50S AND LOWER 60S. 16Z/11 AM SURFACE MAP SHOWS STRONG 998 MB LOW PRESSURE OVER NORTHERN QUEBEC WITH ITS COLD FRONT OFF THE ALTANTIC AND GULF COAST. A SURFACE TROF EXTENDED SW FROM THE LOW INTO NW OH AND SE INDIANA. STRONG 1042 MB ELONGATED HIGH PRESSURE WAS ACROSS THE HIGH PLAINS FROM NORTH TX NORTHWARD ACROSS THE WESTERN DAKOTAS. TIGHT PRESSURE GRADIENT REMAINS OVER IL WITH BREEZY NW WINDS 12 TO 20 MPH AND GUSTS IN THE 20S. TEMPS WERE IN THE LOW TO MID 40S. BROKEN TO OVERCAST LOW CLOUDS WERE DROPPING QUICKLY SSE ACROSS CENTRAL IL TOWARD I-70. THIS ASSOCIATED WITH VERY STRONG UPPER LEVEL TROF EXTENDING FROM HUDSON BAY CANADA SOUTHWARD ACROSS THE GREAT LAKES AND INTO KY/TN. A FEW EMBEDDED SHORT WAVES DROPPING SSE ACROSS THE MIDWEST...ONE OVER SOUTHERN IL AND ANOTHER OVER NORTHERN WI. STEEP LAPSE RATES WITH UPPER LEVEL TROF NEAR IL TO KEEP MOSTLY CLOUDY TO OVERCAST SKIES OVER CENTRAL IL TODAY AND DEVELOP OVER SE IL BY 18Z/1 PM. SHORT WAVE IN NORTHERN WI TO DROP SSE ACROSS NE AND EAST CENTRAL IL THIS AFTERNOON AND BRING A CHANCE OF VERY LIGHT SHOWERS OR SPRINKLES (POSSIBLY FLURRIES FROM PEORIA AND BLOOMINGTON NORTH). BEST CHANCE OF SHOWERS THIS AFTERNOON WILL BE OVER NE IL. BUFKIT MOMENTUM TRANSFERS SHOW NW WIND GUSTS OF 25 TO 35 MPH TODAY WITH HIGHEST WIND GUSTS AT BMI AND CMI. WIDESPREAD LOW CLOUDS COMBINED WITH STRONG NW WINDS TO ONLY ALLOW TEMPS TO CLIMB A DEGREE OR TWO WITH HIGHS TODAY IN THE MID TO UPPER 40S. A FREEZE WARNING CONTINUES OVERNIGHT AND EARLY TUE MORNING WITH A WIDESPREAD HARD FREEZE OVER CENTRAL IL WITH LOWS 25 TO 30F. HUETTL && .AVIATION... ISSUED 615 AM CDT MON OCT 27 2008 DEEP UPR TROF WILL RETAIN CONTROL OVER THE AREA WX THRU THIS TAF PD. ONE SHORTWAVE THAT PASSED THRU OVERNIGHT PRODUCED A SHORT TIME OF MVFR STRATOCU AND -RASN OVER SOME LOCATIONS...BUT THIS FEATURE HAS PASSED E OF THE AREA. ANOTHER WAVE COMING SWD THRU ERN MN/WRN WI MAY CAUSE A FEW MORE SPOTS OF LGT PCPN TDY...BUT CIGS/VSBYS SHOULD REMAIN VFR WITH A BKN DECK OF STRATOCU. SFC PRES GRADIENT REMAINS FAIRLY TIGHT OVER ILLINOIS...SO ANOTHER DAY OF GUSTY NW WNDS IS ON TAP. AFTN GUSTS MAY TOP 30 KT. STRATOCU EXPECTED TO BEGIN BREAKING UP AROUND 00Z TUE...WITH SFC WNDS RELAXING TWD 06Z. 04 && .PREV DISCUSSION... ISSUED 139 AM CDT MON OCT 27 2008 UNSEASONABLY COLD WEATHER TO TAKE HOLD ACROSS CENTRAL ILLINOIS FOR THE NEXT COUPLE OF DAYS...BEFORE WARMER CONDITIONS RETURN FOR THE END OF THE WEEK. 06Z SURFACE CHART SHOWS POLAR FRONT DIVING SOUTHWARD TOWARD THE GULF COAST...WHILE 1042MB HIGH BUILDS SOUTHWARD INTO THE NORTHERN ROCKIES. SHARPLY COLDER AIRMASS CONTINUES TO SPILL INTO CENTRAL ILLINOIS ON GUSTY NORTHWESTERLY WINDS...AS EVIDENCED BY CURRENT TEMPS DIPPING INTO THE UPPER 30S. ALOFT...UPPER LOW CENTERED OVER ONTARIO...WITH DEEP TROUGH DIGGING SOUTHWARD INTO THE GREAT LAKES/MIDWEST. SHORT TERM...TODAY THROUGH WEDNESDAY STRONGLY CYCLONIC FLOW WILL PREVAIL ACROSS THE MIDWEST TODAY...ENSURING MOSTLY CLOUDY SKIES. LATEST SATELLITE LOOPS INDICATE PLENTY OF LOW-LEVEL CLOUDINESS ACROSS CENTRAL ILLINOIS AND EXTENDING WELL UPSTREAM INTO THE EASTERN DAKOTAS. EVEN IF A FEW BREAKS DEVELOP IN THE OVERCAST...COLD TEMPS ALOFT AND RESULTING STEEP LAPSE RATES WILL ALLOW CLOUDS TO QUICKLY FILL BACK IN. MAY EVEN SEE A FEW SPRINKLES OR FLURRIES AT TIMES...AS WEAK IMPULSES CONTINUE TO DROP SOUTHWARD INTO THE MEAN TROUGH POSITION. WILL ALSO BE ANOTHER WINDY DAY...WITH FORECAST SOUNDINGS SUGGESTING WINDS GUSTING TO BETWEEN 25 AND 30MPH. GIVEN THE STRONG CAA AND CLOUD COVER...TEMPS WILL STRUGGLE TO RECOVER. HAVE THEREFORE FOLLOWED THE COOLER MET GUIDANCE NUMBERS MOST CLOSELY...WITH HIGHS MAINLY IN THE MIDDLE 40S. SURFACE HIGH WILL BEGIN TO SHIFT EASTWARD TONIGHT...GRADUALLY PUSHING THE MID AND LOW-LEVEL MOISTURE FURTHER EAST INTO INDIANA. MODELS IN FAIRLY GOOD AGREEMENT WITH THIS PROCESS...WITH THE GFS BEING A BIT FASTER THAN THE NAM-WRF. GIVEN STRENGTH OF UPPER TROUGH AND DEGREE OF CYCLONIC FLOW...PREFER THE SLOWER NAM-WRF. WILL THEREFORE START THE EVENING OUT MOSTLY CLOUDY ACROSS THE BOARD... WITH SKIES CLEARING FROM WEST TO EAST AFTER MIDNIGHT. WITH CLEAR SKIES AND DIMINISHING WINDS...LOW TEMPS TONIGHT WILL DROP WELL BELOW FREEZING ACROSS ALL OF CENTRAL AND SOUTHEAST ILLINOIS. WILL THEREFORE ISSUE A FREEZE WARNING FOR THE ENTIRE KILX CWA...AS TEMPS DIP INTO THE MIDDLE TO UPPER 20S. ANOTHER VERY COOL DAY WILL BE IN STORE FOR TUESDAY...AS SURFACE HIGH REMAINS WEST OF THE MISSISSIPPI RIVER AND LOW-LEVEL FLOW STAYS NORTHWESTERLY. HIGH TEMPS WILL AGAIN STRUGGLE TO RISE THROUGH THE 40S...WHILE EARLY MORNING LOWS WEDNESDAY WILL AGAIN DROP INTO THE 20S. LONG TERM...THURSDAY THROUGH SUNDAY HIGH PRESSURE WILL SHIFT EAST OF THE REGION WEDNESDAY NIGHT AND THURSDAY...ALLOWING SOUTHERLY RETURN FLOW TO DEVELOP AND WARMER TEMPS TO MAKE A COMEBACK ACROSS CENTRAL ILLINOIS. 850MB TEMPS REBOUND TO AROUND 10C ON THURSDAY...SUGGESTING HIGH TEMPS RISING INTO THE LOWER TO MIDDLE 60S. AFTER THAT...THE MEDIUM RANGE MODELS CONTINUE TO INDICATE A NORTHERN STREAM WAVE TRACKING ACROSS SOUTHERN CANADA/NORTHERN GREAT LAKES BY LATE IN THE WEEK. 12Z ECMWF/00Z GFS ARE IN EXCELLENT AGREEMENT CONCERNING THE TRACK AND TIMING OF THIS SYSTEM...AS WELL AS ITS ASSOCIATED COLD FRONT. BOTH MODELS BRING A WEAK COLD FRONT THROUGH ILLINOIS ON FRIDAY...HOWEVER AIRMASS IS TOO DRY TO SUPPORT ANY PRECIP ALONG THE BOUNDARY. AFTER THAT...DRY AND COOL WEATHER CAN BE EXPECTED OVER THE WEEKEND...AS CANADIAN HIGH PRESSURE BUILDS SOUTHWARD INTO THE REGION. BARNES && .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. && $$
