000 FXUS63 KILX 231126 AFDILX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LINCOLN IL 526 AM CST MON NOV 23 2009 .DISCUSSION... ISSUED 217 AM CST MON NOV 23 2009 HIGH PRESSURE RIDGING STILL EXTENDING WEST ACROSS ILLINOIS EARLY THIS MORNING...BUT ITS EFFECTS ARE LESSENING WITH TIME. REGIONAL RADAR MOSAICS SHOWING SOME ECHOES IN FAR WEST CENTRAL ILLINOIS...BUT SURFACE OBS ARE SHOWING THE CLOUDS IN THIS AREA MAINLY AT THE 10000 FOOT LEVEL OR HIGHER...AND LAPS SOUNDINGS IN THIS AREA ARE FAIRLY DRY...SO LITTLE PRECIPITATION IS ACTUALLY REACHING THE GROUND. THE EFFECTS OF A DEVELOPING STORM SYSTEM IN THE TUESDAY-WEDNESDAY TIME FRAME REMAIN THE PRIMARY FORECAST CONCERN...ALONG WITH ANY LINGERING PRECIPITATION ISSUES FOR THANKSGIVING DAY. SHORT TERM...TODAY THROUGH THANKSGIVING DAY... SHORTWAVE OF INTEREST IS CURRENTLY DIGGING ACROSS THE ROCKIES PER LATEST WATER VAPOR IMAGERY. MOST OF THE SHORT-RANGE MODELS ARE FAIRLY UNIFORM IN THE EVOLUTION OF AN ASSOCIATED SURFACE CYCLONE OVER THE CENTRAL PLAINS...LIFTING IT NORTHEAST TO SOUTHERN WISCONSIN BY WEDNESDAY MORNING. THE NAM MODEL IS THE EXCEPTION... WITH A SLOWER AND MORE SOUTHERN TRACK INTO CENTRAL ILLINOIS...SO THIS SOLUTION WILL BE DISCOUNTED AT THIS TIME. TIMING OF THE FRONTAL PASSAGE HAS NOT CHANGED MUCH FROM THE LAST FORECAST PACKAGE...LIKELY TO BE TUESDAY EVENING. LIKELY POPS WILL SPREAD FROM WEST TO EAST ACROSS THE CWA ON TUESDAY...HOLDING OFF ACROSS THE EAST UNTIL AFTERNOON. WILL LINGER HEALTHY POPS INTO THE EVENING...THEN TAPER THEM OFF AFTER MIDNIGHT AS THE DRY SLOT WORKS ITS WAY ACROSS THE AREA. A SEPARATE SHORTWAVE WILL QUICKLY DIVE SOUTH OUT OF MANITOBA WEDNESDAY MORNING...BECOMING THE DOMINANT CLOSED UPPER LOW AS THE ORIGINAL LOW SHEARS OUT AS IT LIFTS NORTHEAST. ALL MODELS HAVE THIS FEATURE ACROSS NORTHERN ILLINOIS BY THURSDAY MORNING. LINGERING LIGHT RAIN IS EXPECTED ON WEDNESDAY PRIMARILY OVER THE NORTHERN CWA...IN THE CIRCULATION OF THE DEPARTING SURFACE LOW. HOWEVER...ANOTHER TROUGH/COLD FRONT WILL QUICKLY APPROACH FROM THE NORTHWEST LATE WEDNESDAY NIGHT...AND SWING THROUGH THE AREA ON THANKSGIVING DAY. THICKNESS LEVELS IN THE 1000-500MB LAYER PLUNGE LOW ENOUGH TO SUPPORT A TRANSITION TO SNOW WEDNESDAY NIGHT...WITH BUFKIT SOUNDINGS ALSO SHOWING THIS TREND. PRECIPITATION LIKELY TO CONTINUE INTO THURSDAY AS EITHER RAIN OR SNOW...ALTHOUGH THE LONGER RANGE MODELS ARE A BIT DIVIDED ON THE SPEED OF THIS FRONT...THUS HAVE DIFFERING OPINIONS ON THE AMOUNT OF PRECIPITATION INVOLVED. CURRENTLY WILL GO WITH 30 POPS FOR THIS PERIOD AND LET THE LATER MODEL RUNS TRY TO RESOLVE THIS ISSUE. LONG TERM...FRIDAY THROUGH SUNDAY... GFS AND ECMWF BOTH AGREE ON A SURFACE RIDGE PUSHING EAST ACROSS THE CENTRAL CONUS ON FRIDAY...WITH THE UPPER LEVEL FLOW BECOMING MORE SOUTHWESTERLY BY SUNDAY MORNING AS A PAIR OF SHORTWAVES MOVE THROUGH THE PLAINS AND SOUTHERN ROCKY MOUNTAINS. ANY ASSOCIATED PRECIPITATION WOULD LIKELY HOLD OFF UNTIL AT LEAST SUNDAY...BUT THE TIMING IS A BIT IN QUESTION WITH DIFFERING SOLUTIONS ON THE SPEED OF THE SURFACE FRONT. GEELHART && .AVIATION... ISSUED 515 AM CST MON NOV 23 2009 TWO AREAS OF CONCERN THIS FORECAST PERIOD. THE FIRST BEING WITH THE PATCHY AREAS OF FOG THIS MRNG...WITH THE SECOND CHALLENGE BEING WITH THE MVFR CIGS TRACKING NWD OUT OF SOUTHEAST MO AND WRN KY THIS MRNG. LIGHT WIND FLOW COUPLED WITH ABUNDANT LOW LEVEL MOISTURE FROM WET GROUND HAS LED TO SOME PATCHY MVFR/IFR FOG...ESP ACRS THE EAST. WL CARRY TEMPO GROUPS FOR THE FOG THRU AT LEAST 15Z AND THAT MAY NOT BE LONG ENOUGH AS THE EXTENSIVE MID AND HIGH LEVEL CLOUD COVER MAY LIMIT THE AMT OF MIXING THIS MRNG AND KEEP THE LOWER VSBYS IN FOR A BIT LONGER COMPARED WITH THE PAST FEW MRNGS. ONCE THE FOG DISSIPATES LATE THIS MRNG INTO EARLY THIS AFTN...WL SEE A BRIEF PERIOD OF VFR CONDITIONS BEFORE OUR ATTENTION TURNS TO THE MVFR AND LOCAL IFR CIGS TO OUR SOUTH FOR THIS EVENING AND OVERNIGHT. BASED ON THE PRESENT MOVEMENT OF THE LOWER CIGS TO OUR SOUTH...IT APPEARS THEY SHOULD BEGIN TO AFFECT SPI AND DEC EARLY THIS EVENING...SHORTLY AFTR 00Z...AND POINTS FURTHER NORTH AN HOUR OR TWO LATER. SEEING A LOT OF CIGS AOB 1000 FEET ACRS ARKANSAS AND SW KY EARLY THIS MRNG WITH THE LOW LEVEL FLOW EXPCTD TO BRING THAT NWD DURING THE DAY. MAY EVEN SEE SOME PATCHY DRIZZLE MOVE IN OVERNIGHT AS MODELS DO INDICATE SOME WEAK LIFT PUSHING ACRS THE AREA DURING THE EARLY MRNG HOURS...WHICH MAY ACTUALLY BRING CIGS AND VSBYS DOWN FURTHER THAN CURRENTLY INDICATED. WL CONTINUE TO MONITOR FOR THOSE TRENDS DURING THE DAY. SMITH && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$