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000 FXUS63 KILX 230257 AFDILX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LINCOLN IL 857 PM CST SUN NOV 22 2009 .DISCUSSION... ISSUED 857 PM CST SUN NOV 22 2009 TEMPS ARE FALLING LITTLE FURTHER AND SOME SITES ALREADY CLOSE TO FORECASTED MINS...MAINLY IN THE NORTHEAST. HIGH CLOUDS CONTINUE OVER THE WEST AND EASTERN PARTS OF THE CWA SO THIS SHOULD CAUSE TEMPS TO BECOME STEADY OVERNIGHT. SO WILL BE MAKING SOME ADJUSTMENTS TO TEMP GRIDS TONIGHT. NOT SURE YET IF IT WILL AFFECT TEXT PRODUCT...BUT IF DOES...SHOULD ONLY AFFECT EASTERN AND NORTHEAST GROUPS. AUTEN && .AVIATION... ISSUED 527 PM CST SUN NOV 22 2009 VFR CONDITIONS WILL CONTINUE TONIGHT BUT THEN LIGHT FOG WILL DEVELOP AT ALL SITES AROUND 06Z LIKE IT DID LAST NIGHT. LIGHT FOG WILL BURN OFF IN THE MORNING FOLLOWED BY A MID DECK ADVECTING INTO THE AREA. PIA...BMI AND SPI COULD SEE SOME LOWER SC CLOUDS AT 3.5KFT WHILE DEC AND CMI WILL JUST SEE A MID DECK TOMORROW. LIGHT EAST WINDS WILL BECOME SOUTHEAST TOMORROW AND CONTINUE INTO THE AFTERNOON. AUTEN && .PREV DISCUSSION... ISSUED 309 PM CST SUN NOV 22 2009 A PLEASANT FALL DAY IS UNFOLDING ACROSS CENTRAL AND SOUTHEAST ILLINOIS...COURTESY OF A LARGE AREA OF HIGH PRESSURE CENTERED OVER NEW ENGLAND. ONE MORE PRETTY NICE DAY IS ON TAP UNTIL SLOW MOVING STORM SYSTEM ARRIVES FOR TUESDAY AND LINGERS IN THE AREA THROUGH THANKSGIVING. THIS SLOW MOVING STORM SYSTEM...AND THE ASSOCIATED PRECIPITATION THREAT AND IMPACT ON TEMPERATURES...IS OUR PRIMARY FORECAST CONCERN TODAY. 12Z MODELS IN REASONABLE AGREEMENT THROUGH THE SHORT TERM. HOWEVER...THEY ARE TRENDING SLOWER WITH OUR APPROACHING STORM SYSTEM. HAVE TRENDED THE FORECAST TOWARD THE MIDDLE OF THE MODEL ENVELOPE...WHICH IS QUICKER THAN THE NAM....BUT SLOWER THAN THE GFS. SHORT TERM...TONIGHT THROUGH WEDNESDAY...OUR STORM SYSTEM IS ALREADY BEGINNING TO DEVELOP OVER THE CENTRAL PLAINS...AS EVIDENCED BY THE LOW PRESSURE CENTER STARTING TO DEVELOP OVER KANSAS. HOWEVER...IT WILL NOT REALLY DEEPEN OR START MOVING OUR DIRECTION UNTIL IT INTERACTS WITH THE VIGOROUS UPPER WAVE CURRENTLY DIVING THROUGH THE PACIFIC NORTHWEST. IN THE MEANTIME... QUIET AND MILD LATE NOVEMBER CONDITIONS WILL PERSIST INTO MONDAY NIGHT AS RETURN FLOW INCREASES ON THE BACK SIDE OF THE DEPARTING AREA OF HIGH PRESSURE. THE DIURNAL TEMPERATURE RANGE MAY BE A BIT SMALLER THROUGH MONDAY NIGHT THAN THE PAST FEW DAYS AS THE SYSTEM BEGINS TO APPROACH AND CLOUD COVER INCREASES. THE APPROACHING STORM AND TRAILING FRONTAL BOUNDARY IS STILL EXPECTED TO MOVE THROUGH THE REGION ON TUESDAY...BUT THE FRONTAL SPEED HAS SLIPPED BY ABOUT 6 HOURS. SO...AN 18Z TUE-06Z WED PASSAGE LOOKS MORE LIKELY NOW THAN THE PREVIOUSLY EXPECTED 12Z TUE-00Z WED PASSAGE. THE MAIN SURFACE LOW WILL LIFT INTO THE GREAT LAKES TUESDAY NIGHT...WITH THE TRAILING COLD FRONT EXPECTED TO CLEAR THE FORECAST AREA BY AROUND 06Z WEDNESDAY. THIS SYSTEM SHOULD BE PRETTY DYNAMIC...THOUGH ALREADY OCCLUDED BY THE TIME IT GETS HERE...WITH DECENT JET FORCING PROGGED OVER THE FORECAST AREA ON TUESDAY COUPLED WITH THE SURFACE FROPA. HAVE KEPT LIKELY RAIN CHANCES IN THE WESTERN HALF OF THE FORECAST AREA FOR TUESDAY...WITH THE EASTERN HALF PROBABLY NEEDING A BUMP ONCE THE TIMING IS MORE FIRM. HOWEVER...IT IS HARD TO JUSTIFY LIKELY POPS IN THE EAST AT THIS TIME AS THE FROPA STILL APPEARS POSSIBLE IN MORE THAN ONE FORECAST PERIOD. ONCE THE FRONT CLEARS THE FORECAST AREA TO THE EAST...THERE SHOULD BE A LULL IN THE PRECIPITATION THREAT. WHILE WRAP AROUND PRECIPITATION IS POSSIBLE WEDNESDAY...THE BULK OF IT SHOULD HOLD OFF UNTIL THE EXTENDED RANGE OF THE FORECAST PERIOD. THE SLOWER PROGRESSION OF THE SYSTEM AND ASSOCIATED ARRIVAL OF COLDER AIR SHOULD KEEP ANY PRECIPITATION FALLING AS RAIN THROUGH WEDNESDAY. LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY...MODELS/ENSEMBLES INITIALLY IN FAIRLY GOOD AGREEMENT WITH RESPECT TO FEATURES EXPECTED TO IMPACT FORECAST AREA. HOWEVER...SPREAD INCREASES SIGNIFICANTLY FROM FRIDAY TO THE END OF THE PERIOD. UNFORTUNATELY...ONE ITEM THAT HAS DEVELOPED SINCE YESTERDAY IS THAT IT LOOKS INCREASINGLY LIKELY THAT PRECIPITATION...MOSTLY SNOW...IS POSSIBLE ON THANKSGIVING. THE SURFACE LOW THAT BROUGHT THE RAINS ON TUESDAY WILL STILL BE OVER THE GREAT LAKES AT THE START OF THE PERIOD. A STRONG UPPER WAVE WILL DIVE DOWN THE BACKSIDE OF THIS VERTICALLY STACKED SYSTEM...LIKELY PRODUCING A ROUND OF PRECIPITATION LATE WEDNESDAY NIGHT INTO THANKSGIVING DAY. SOUNDING PROFILES/THICKNESS SCHEMES SUGGEST THAT ALL THE WARM AIR WILL BE NEAR SURFACE BASED WHEN THIS PRECIPITATION WOULD FALL. SO THE PRECIPITATION WILL BE FALLING AS SNOW...AND IT APPEARS THAT THE ABOVE FREEZING NEAR SURFACE LAYER WILL BE TOO SHALLOW TO MELT THE SNOW BEFORE IT REACHES THE GROUND. HOWEVER...AT THIS POINT... LITTLE OR NO ACCUMULATION IS EXPECTED WITH THE SNOW. UPPER/SURFACE RIDGING START TO BUILD IN FRIDAY INTO SATURDAY ENDING THE PRECIPITATION AND ALLOWING TEMPERATURES TO MODERATE A BIT. THE ARRIVAL OF THE NEXT WEATHER SYSTEM IS MUCH LESS CLEAR AT THIS TIME. THE GFS SOLUTIONS TEND TO DEVELOP A MORE PHASED DEEP TROF OVER EASTERN NORTH AMERICA...WHILE THE ECMWF SPLITS THE FLOW AND CUTS OFF A LOW OVER THE SOUTHWEST UNITED STATES. THIS RESULTS IN THE GFS BEING QUICKER AND STRONGER WITH THE NEXT SYSTEM BY LATE IN THE WEEKEND. WILL CONTINUE TO SIDE WITH THE MORE CONSISTENT ECMWF AND LEAVE THE END OF THE WEEKEND DRY AT THIS TIME. BAK && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$
