Issued by NWS Central Illinois
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000 FXUS63 KILX 270639 AFDILX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LINCOLN IL 139 AM CDT MON OCT 27 2008 .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 && .AVIATION... ISSUED 1152 PM CDT SUN OCT 26 2008 GUSTY WINDS HAVE HELD UP A BIT BETTER THAN PREVIOUSLY EXPECTED. WHILE THEY HAVE DECREASED...APPARENTLY THE PRESSURE GRADIENT...IN COMBINATION WITH SUBSIDENCE IN THE STRONG COLD ADVECTION PATTERN... IS COMPENSATING FOR THE LOSS OF DIURNAL MIXING. SO...EXPECT GUSTY NORTHWEST WINDS TO LINGER UNTIL DIURNAL HEATING HIS LOST MONDAY EVENING...AROUND THE SAME TIME THE SURFACE PRESSURE GRADIENT BEGINS TO RELAX. OTHERWISE...WRAP AROUND CLOUDS WILL CONTINUE TO SPREAD ACROSS THE TERMINALS THROUGH MONDAY EVENING...WHEN THEY SHOULD TEND TO SCATTER OUT. LOW END VFR CIGS SHOULD PREVAIL...BUT A PERIOD OF MVFR CIGS IS LIKELY FOR THE NEXT FEW HOURS... ESPECIALLY ACROSS KPIA/KBMI/KCMI TERMINALS. A FEW FLURRIES OR SPRINKLES ARE ALSO POSSIBLE...BUT WILL NOT BE HEAVY ENOUGH TO CAUSE A VISIBILITY RESTRICTION. BAK && .ILX WATCHES/WARNINGS/ADVISORIES... FREEZE WARNING UNTIL 9 AM CDT THIS MORNING FOR ILZ027>031- 036>038-040>057-061. && $$
