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000 FXUS63 KILX 261739 AFDILX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LINCOLN IL 1239 PM CDT SUN OCT 26 2008 .DISCUSSION... ISSUED 1044 AM CDT SUN OCT 26 2008 THE BIG STORY FOR TODAY INTO THIS EVENING WILL BE THE INCREASING WIND AND THEN FREEZING TEMPS OVERNIGHT IN CENTRAL IL. AT 15Z THE COLD FRONT WAS LOCATED FROM NW IND TO JUST WEST OF CHAMPAIGN TO ST. LOUIS. THE WIND WAS JUST STARTING TO INCREASE IN NW AND WEST CENTRAL IL LATE THIS MORNING AT THE LEADING EDGE OF THE LOW LEVEL COLD AIR ADVECTION/GREATEST SURFACE PRESSURE RISES. THE VWP FROM THE ILX RADAR WAS SHOWING 30-35 KNOT WINDS IN THE LOWEST FIVE THOUSAND FEET. UPSTREAM LOCATIONS INDICATE THAT THIS WILL INCREASE A BIT DURING THE AFTERNOON AND MIX DOWN TO THE SURFACE DURING THE AFTERNOON AND EVENING HOURS. STILL EXPECT THE MIXING TO DECREASE SHORTLY AFTER SUNSET...SO FOR NOW WILL KEEP THE WIND ADVISORY EXPIRATION TIME AT 9 PM CDT. UPDATED THE FORECAST AND GRIDS TO REMOVE THE MORNING MENTION OF LIGHT RAIN SHOWERS AND TO ADJUST THE SKY COVER AND HOURLY TEMPS. QUICK LOOK AT THE NUMERICAL GUIDANCE AND UPSTREAM OBS SHOWS THAT THE FREEZE WARNING STILL LOOKS GOOD FOR TONIGHT...SO NO CHANGES EXPECTED THERE. && .AVIATION... ISSUED 1239 PM CDT SUN OCT 26 2008 THERE ARE TWO MAIN CONCERNS INCORPORATED INTO THE 18Z TAF ISSUANCE. FIRST IS THE VERY WINDY WEATHER EXPECTED IN CENTRAL AND EASTERN IL THIS AFTERNOON. A TIGHT PRESSURE GRADIENT BETWEEN A STRONG LOW IN ONTARIO AND HIGH PRESSURE RIDGING DOWN INTO THE HIGH PLAINS WILL RESULT IN A WEST-NORTHWEST WIND INCREASING INTO THE 22 TO 30 KNOT RANGE...WITH GUSTS UP TO 40 KNOTS THIS AFTERNOON INTO EARLY THIS EVENING. BUFKIT SOUNDINGS INDICATE THAT THE MIXING THAT IS TRANSPORTING THE LOW LEVEL WINDS DOWN TOWARD THE SURFACE WILL WEAKEN A BIT AROUND 01-03Z. THUS...I KEPT THE TREND OF THE PREVIOUS TAFS BY DROPPING THE SUSTAINED WIND TO ABOUT 15-20KTS WITH GUSTS OF 25-30KTS UNTIL MIDNIGHT OR SHORTLY THEREAFTER. THE NEXT MAIN CONCERN IS THE INCREASE IN LOWER CLOUDS THAT IS ANTICIPATED AFTER MIDNIGHT. LOW LEVEL HUMIDITY PROJECTIONS... TIME-HEIGHT CROSS SECTIONS AND EXTRAPOLATION OF A FAST MOVING AREA OF STRATOCUMULUS IN NORTH DAKOTA ALL POINT TO A BKN-OVC DECK OF CLOUDS MOVING IN AROUND 06Z. AT THIS TIME THE AFOREMENTIONED MODEL GUIDANCE POINTS TO CEILINGS AROUND 4K FT...STILL IN THE VFR CATEGORY. WILL KEEP AN EYE ON THIS THOUGH SINCE THERE IS THE POSSIBILITY THAT THE CEILINGS MAY DIP INTO THE MVFR CATEGORY FOR A PERIOD OF TIME TOWARD DAYBREAK. MILLER && .PREV DISCUSSION... ISSUED 321 AM CDT SUN OCT 26 2008 SHORT TERM MODELS IN FAIRLY GOOD AGREEMENT AND ARE CONSISTENT WITH PREVIOUS RUNS ON HANDLING OF THE FAST MOVING COLD FRONT TODAY. ONLY DIFFERENCE SEEN IS WITH THEIR HANDLING OF THE PCPN MOVING ACROSS IOWA AT THE MOMENT. GFS SEEMS TO HANDLE THIS BETTER THAN THE NAM-WRF...THOUGH NOT AS WELL AS WOULD HAVE HOPED. ANY RATE...RH FIELDS ON GFS LOOKS BETTER THAN NAM SO WILL LEAN THAT DIRECTION FOR THIS MORNING. A BLEND OF THE MODELS FOR THE REST LOOKS FINE. IN THE LONG TERM...THE ECMWF STILL LOOKS GOOD. MAIN CONCERN THIS PACKAGE IS WITH PCPN THIS MORNING...GUSTY WINDS TODAY AND FREEZING TEMPS TONIGHT AND MONDAY NIGHT. LONG TERM CONCERNS IS SPEED OF ANY WARM UP. SHORT TERM...TODAY THROUGH TUESDAY NIGHT COLD FRONT HAS REACHED THE IOWA/ILLINOIS BORDER AND IS QUICKLY MOVING SOUTHEAST INTO THE AREA. BEHIND THE FRONT IS AN AREA OF SHOWERS THAT WILL AFFECT MOST OF THE CWA THIS MORNING...PRIOR TO 18Z. WINDS WILL BECOME NORTHWEST AND INCREASE TO 25-35 MPH WITH GUSTS TO AROUND 45 MPH. ADVISORY STILL MAKES SENSE AND WILL CONTINUE UNTIL 02Z THIS EVENING. SKIES WILL BECOME MOSTLY SUNNY BEHIND FRONT/PCPN BUT GUSTY WINDS WILL MAKE IT QUITE CHILLY. WINDS SHOULD DECOUPLE SOME THIS EVENING BUT GRADIENT WILL REMAIN TIGHT COULD STILL BE SOME GUSTS AT NIGHT...BUT NOT ADVISORY CRITERIA. A SECONDARY 500MB AND SFC TROUGH WILL DROP INTO THE REGION FOR MONDAY AND THIS COULD BRING ADDITIONAL PCPN TO THE REGION. 850 TEMPS WILL BE BELOW ZERO WHICH MEANS PCPN COULD BE FLURRIES EARLY CHANGING TO ALL SPRINKLES OR A MIX. CONFIDENCE IS NOT HIGH WITH THIS AND DUE TO LACK OF MOISTURE...BELIEVE CHANCES ARE SMALL. SO HAVE GONE WITH SLIGHT CHANCE OF PCPN FOR MONDAY...WHICH WILL NOT SHOW UP IN TEXT FORECAST. AFTER THIS...THE LARGE HIGH PRESSURE WILL FINALLY BUILD INTO THE REGION FOR TUESDAY AND THE REST OF THE WEEK...WITH DRY WEATHER. COLD AIR ADVECTION WILL BE THE RULE FOR MOST OF THE PERIOD AS 500MB TROUGH DEVELOPS IN THE EASTERN US AND A COLD HIGH PRESSURE SLIDES DOWN INTO THE PLAINS. ILLINOIS WILL BE INFLUENCE BY NORTHERLY FLOW FOR THE NEXT 3 DAYS GIVING US BELOW NORMAL TEMPS THROUGH THE PERIOD. TEMPS WILL GET COLD TONIGHT...BUT BREEZY WINDS WILL KEEP THEM FROM FALLING TOO FAR. THE STRONG CAA WILL STILL BRING BELOW FREEZING TEMPS TO MOST OF THE CWA TONIGHT. THEN WE`LL SEE HIGH TEMPS MONDAY 15-20 DEGREES BELOW NORMAL. A HARD FREEZE WILL BE IN STORE FOR MONDAY NIGHT OVER THE ENTIRE CWA AS SKIES WILL BE CLEAR...WINDS WILL BE LIGHT AND A SECOND SHOT OF COLD AIR WILL HAVE DROPPED INTO THE AREA. TEMPS WILL REMAIN BELOW NORMAL FOR TUE AND TUE NIGHT. GUIDANCE TEMPS NOT TOO BAD BUT DID UNDERCUT HIGHS FOR MON AND TUE IN SOME AREAS. LONG TERM...WEDNESDAY THROUGH SATURDAY HIGH PRESSURE WILL GRADUALLY SHIFT INTO SOUTHEASTERN US THROUGH THE PERIOD AND BRING SOUTHWESTERLY FLOW BACK TO ILLINOIS. THIS SHOULD BRING RETURN OF WAA TO THE AREA FOR THE PERIOD. GFS SEEMS FAST WITH BRING THE NEXT FRONT INTO THE AREA WHILE ECMWF APPEARS TO BE THE BETTER SOLUTION WHICH IS SLOWER. WARM UP IN THE AREA WILL LIKELY BE SLOWER THAN MEX GUIDANCE INDICATES SO WILL UNDERCUT MEX NUMBERS BY SEVERAL DEGREES. AUTEN && .ILX WATCHES/WARNINGS/ADVISORIES... FREEZE WARNING FROM 1 AM TO 9 AM CDT MONDAY FOR ILZ027>031- 036>038-040>057-061. WIND ADVISORY UNTIL 9 PM CDT THIS EVENING FOR ILZ027>031-036>038- 040>057-061. && $$
