Issued by NWS Central Illinois
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000 FXUS63 KILX 221135 AFDILX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LINCOLN IL 535 AM CST SUN NOV 22 2009 .DISCUSSION... ISSUED 220 AM CST SUN NOV 22 2009 LATEST SURFACE MAP STILL SHOWING THE CWA UNDER THE INFLUENCE OF HIGH PRESSURE RIDGING...EXTENDING FROM THE EASTERN GREAT LAKES REGION. MID-LEVEL CLOUD DECK HAS BEEN TRYING TO ERODE ON ITS EASTERN FLANK...BUT WAS INCREASING AGAIN IN WEST CENTRAL ILLINOIS INTO MISSOURI. FOG ISSUES HAVE MAINLY BEEN LIMITED TO SELECT LOW LYING AREAS NEAR THE INDIANA BORDER...BUT 3 TO 5 MILE VISIBILITIES ARE NOT UNUSUAL EAST OF I-55. TEMPERATURES HAVE BEEN ABLE TO STAY UP HIGHER THAN LAST NIGHT WITH A BIT OF A SOUTHEAST COMPONENT TO THE WIND...BUT SOME 30S WERE FOUND IN A FEW AREAS EAST OF I-55. MAIN ISSUE WITH THE FORECAST CONTINUES TO INVOLVE A STORM SYSTEM MOVING THROUGH THE MID-MISSISSIPPI VALLEY TOWARD MIDWEEK. MODELS ARE IN DECENT AGREEMENT WITH THE UPPER LEVEL FEATURES...AND ARE COMING INTO BETTER ALIGNMENT WITH THE SPEED OF THE SURFACE FRONT AND ASSOCIATED LOW. SHORT TERM...TODAY THROUGH TUESDAY... HIGH PRESSURE RIDGING EXPECTED TO REMAIN IN PLACE THROUGH TODAY...THEN BEGIN TO BREAK DOWN THIS EVENING AS THE LOW/FRONT ORGANIZES OVER THE PLAINS. ANOTHER MILD COUPLE OF DAYS EXPECTED AS THE SOUTHEAST FLOW BECOMES MORE ENTRENCHED...WITH HIGHS CLOSE TO 60. MAIN FEATURE OF INTEREST IS CURRENTLY JUST OFF THE OREGON COAST PER LATEST WATER VAPOR IMAGERY. THIS WAVE SHOULD MOVE INTO THE CENTRAL PLAINS BY LATE MONDAY EVENING AND DEEPEN INTO A CLOSED LOW...WHICH WILL PUSH EAST INTO THE CWA BY EARLY WEDNESDAY MORNING. ECMWF AND CANADIAN MODELS DEEPEN THE SURFACE LOW MUCH MORE RAPIDLY AND STRONGER THAN THE NAM/GFS/SREF...BUT ARE SIMILAR IN THE GENERAL TRACK INTO THE WISCONSIN/ILLINOIS BORDER REGION THROUGH TUESDAY NIGHT AS THE LOW OCCLUDES. MAIN FRONTAL BOUNDARY EXPECTED TO PASS THROUGH THE AREA TUESDAY EVENING. NET RESULT IS TO LIMIT POPS TO THE WESTERN CWA MONDAY NIGHT AFTER MIDNIGHT...AND CONTINUE WITH LIKELY POPS MUCH OF THE AREA LATER TUESDAY. HIGHEST POPS TUESDAY NIGHT TO BE NEAR THE FRONT...BUT WILL BE PRESENT EVERYWHERE DUE TO THREAT OF WRAPAROUND SHOWERS BEHIND THE LOW. LONG TERM...WEDNESDAY THROUGH SATURDAY... SECOND UPPER LOW EXPECTED TO PLUNGE SOUTHWARD INTO THE LOWER MISSOURI VALLEY ON WEDNESDAY...PUSHING EAST ACROSS THE MIDWEST THE REMAINDER OF THE WEEK. GFS/ECMWF BOTH SHOWING A SURFACE TROUGH/FRONT SWINGING THROUGH THE MIDWEST ON THANKSGIVING DAY...FOLLOWED BY HIGH PRESSURE BUILDING IN FROM THE WEST. MAIN CONCERN WILL BE WITH POPS DURING WEDNESDAY AND THURSDAY. HAVE CONTINUED LOW CHANCE POPS ACROSS THE NORTHERN CWA FOR WEDNESDAY...AND ADDED SLIGHT CHANCES TO THIS AREA FOR THANKSGIVING DAY. BUFKIT SOUNDINGS INDICATE ANY PRECIPITATION ON WEDNESDAY WOULD BE TRANSITIONING FROM RAIN TO SNOW BY EVENING...AND THURSDAY PRECIPITATION WOULD MOST LIKELY BE IN THE FORM OF SNOW. GEELHART && .AVIATION... ISSUED 525 AM CST SUN NOV 22 2009 MAIN FORECAST CONCERN THIS PERIOD WILL BE WITH FOG AND ITS AFFECT ON VSBYS FOR THE FIRST FEW HOURS OF THIS FCST PERIOD...OTHERWISE VFR CONDITIONS WILL PREVAIL. BAND OF MID CLOUDS (6500-8500 FEET) LOCATED OVR EXTREME WRN IL EXPECTED TO REMAIN JUST WEST OF PIA AND SPI TODAY...WHILE THE RMDR OF THE SITES WL SEE ONLY A SCATTERING OF HIGH CLOUDS DURING THE DAY. FORECAST SOUNDINGS SUGGEST THE MAIN BAND OF MID LEVEL CLOUDS THAT HAVE BEEN STREAMING NWD OUT OF MO ACRS WRN IL WILL CONTINUE THAT TREND INTO THIS EVENING...WHILE A WEATHER DISTURBANCE ACRS THE GULF COAST STATES SPREADS SOME CIRRUS NWD INTO CNTRL IL DURING THE DAY AND ESP TNT. SURFACE WINDS WL REMAIN FROM AN EAST TO SOUTHEAST DIRECTION INTO TNT WITH SPEEDS ARND 10 KTS TODAY AND FROM 5 TO 10 KTS TNT. WITH ABUNDANT LOW LVL MOISTURE STILL IN PLACE ACRS THE REGION...AND DECOUPLING OF THE WINDS TNT WL LEAD TO AREAS OF FOG. WL BRING IN 4-5 MILE VSBYS ARND 06Z BUT COULD SEE THOSE DROP EVEN LOWER TWDS SUNRISE MONDAY. SMITH && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$