000 FXUS63 KILX 250303 AFDILX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LINCOLN IL 903 PM CST FRI DEC 24 2004 .DISCUSSION...LATEST SURFACE ANALYSIS HAD HIGH PRESSURE CENTERED OVER THE OHIO VALLEY...WITH THE ASSOCIATED RIDGE AXIS JUST EAST OF FORECAST AREA. MEANWHILE...LOW PRESSURE WAS DEVELOPING OVER THE CANADIAN PRAIRIES...WITH A WARM FRONT EXTENDING SOUTHEAST INTO THE CENTRAL PLAINS. IN ADDITION...A TROF EXTENDED FROM THE WARM FRONT OVER THE DAKOTAS INTO IOWA. ALOFT...BROAD CYCLONIC FLOW WAS OVER THE NORTHEAST UNITED STATES...WITH NUMEROUS IMPULSES EMBEDDED IN THE FLOW. A LARGE AREA OF CLOUDS AND SCATTERED FLURRIES IS ASSOCIATED WITH AN IMPULSE OVER IOWA. THE LEADING EDGE OF THE CLOUDS WITH THIS FEATURE HAS ALREADY REACHED THE I-55 CORRIDOR AND CONSIDERABLY SLOWED THE TEMPERATURE FALL THERE. THE TEMPERATURE FALL HAS ALSO BEEN SLOWED BY AN INCREASING SOUTHWEST FLOW ON THE BACK SIDE OF THE SURFACE RIDGE AXIS. GOING FORECAST GENERALLY IN GOOD SHAPE. WILL BRING THE CLOUDS IN A BIT QUICKER PER LATEST SATELLITE TRENDS AND ADD FLURRIES AS IOWA IMPULSE SLIDES THROUGH OVERNIGHT. WILL ALSO MAKE A FEW TEMPERATURE TWEAKS...RAISING THEM A BIT IN THE WEST WITH THE CLOUDS ALREADY IN PLACE AND LOWERING THEM A BIT IN THE EAST PER LATEST TRENDS (ESPECIALLY OVER THE SNOW PACK). && .PREV DISCUSSION...MAIN FORECAST CONCERNS AT LEAST IN THE SHORT TERM WILL BE AMOUNT OF WARMING THE NEXT SVL DAYS...ESP OVR SNOW COVERED AREAS OF SE IL AND ANY LIGHT SNOWS THAT MAY ACCOMPANY THE MODERATING TEMPS ON XMAS. NO SIGNIFICANT MODEL DIFFERENCES SEEN INTO EARLY NEXT WEEK AS THE GFS HAS COME AROUND TO WHAT THE ETA HAD SHOWN YESTERDAY REGARDING THE WEAK FRONTAL PASSAGE ON SUNDAY. WL TEND TO BLEND THE ETA AND MAV GUID NUMBERS THIS FCST PERIOD WITH THE ETA 2 METER TEMPS A BIT TOO AGGRESSIVE (COLD) OVER THE SNOW IN SE IL. SHORT TERM...TONIGHT THROUGH MONDAY NIGHT LATEST SURFACE ANALYSIS INDICATING HIGH PRESSURE SLOWING PULLING AWAY FROM THE MIDWEST EARLY THIS AFTERNOON WITH TEMPERATURES INCHING THEIR WAY INTO THE LOW TO MID TEENS. MORNING UPPER AIR STILL SHOWING THE CORE OF THE COLD AIR TO OUR NORTH (-30C AT 850 MB AND -42C NORTH OF LAKE SUPERIOR AT 500 MB) WITH IMPRESSIVE WARMING TAKING PLACE OVER THE NRN AND CNTRL PLAINS THIS AFTN. MODELS INDICATE AS LOW AND MID LVL WARM ADVECTION DVLPS ACRS OUR AREA TNT CLOUDS WL INCREASE FROM THE NW WITH THE CHANCE FOR FLURRIES TO MOVE IN AFTER MIDNIGHT. COLDEST TEMPS WL BE REALIZED BEFORE MIDNIGHT AND ESPECIALLY OVER THE SNOW COVERED AREAS OF OUR SE COUNTIES (I-70 CORRIDOR) WHICH MAY SEE THE MERCURY DROP TO -5 OR COLDER FOR A TIME THIS EVENING BEFORE THE CLOUDS AND LIGHT SOUTHERLY FLOW DEVELOPS. SHORTWAVE TROF FCST TO PUSH RAPIDLY SE ACRS THE NRN PLAINS SAT MORNING AND INTO THE MIDWEST BY AFTN OR EARLY EVENING WITH 290K ISENT SFCS INDICATING LOWERING PDEF AND SOME FAIRLY DECENT LIFT FOR ABOUT A 6 HOUR PERIOD TMRW AFTN AHEAD OF SHORTWAVE. WL INCLUDE 30 POPS FOR A PERIOD OF LIGHT SNOW TMRW AFTN...MAINLY ALONG AND NORTH OF SPI TO MTO LINE WITH FLURRIES PSBLY LINGERING INTO SAT EVENING. AS SHORTWAVE SHIFTS TO OUR EAST LATER SAT NIGHT...FRONTAL BOUNDARY WILL PUSH ACRS THE FCST AREA SUN MRNG EFFECTIVELY SHIFTING OUR WINDS INTO THE NE AND HOLDING BACK OUR EXPECTED WARMUP FOR A DAY OR SO. WEAK ARCTIC HIGH FCST TO SHIFT EAST ACRS THE SRN LAKES SUN AND INTO MONDAY MORNING BEFORE SOUTHERLY WINDS RETURN BY AFTN WHICH SHOULD HELP PUSH TEMPERATURES INTO THE 30S OVER MOST OF THE FCST AREA. LONG TERM...TUESDAY THROUGH FRIDAY ECMWF MODEL ONCE AGAIN USED FOR THE EXTENDED PERIOD AS IT HAS SHOWN MORE CONSISTENCY IN HANDLING THE MAJOR PATTERN CHANGE FOR NEXT WEEK. A LONGWV TROF WILL SETTLE INTO THE WRN U.S. HELPING TO ESTABLISH A FAIRLY STRONG POSITIVE HEIGHT ANOMALY ACRS THE ERN TWO THIRDS OF THE NATION. THIS TRANSLATES TO ABOVE NORMAL TEMPERATURES WITH PRECIP CHANCES CUT BACK UNTIL THURSDAY AND FRIDAY WHEN LEAD SHORTWV ENERGY IS FCST TO EJECT OUT OF THE LNGWV TROF AND INDUCE CYCLOGENESIS ACRS THE PLAINS AND PUSH A FRONTAL BOUNDARY TOWARDS THE MIDWEST. MODELS HINTING AT ANOTHER WEAK FRONTAL PASSAGE LATE TUE OR WEDNESDAY OVR PARTS OF CNTRL IL BUT ANY SENSIBLE WEATHER WITH THIS WILL BE NIL. && .ILX WATCHES/WARNINGS/ADVISORIES... .IL...NONE. && $$ BAK/SMITH