000 FXUS63 KLOT 310931 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO IL 331 AM CST THU JAN 31 2008 .DISCUSSION... 311 PM CST MAIN FOCUS OVER THIS FORECAST PERIOD REVOLVES AROUND THE DEVELOPING STORM SYSTEM IN THE SOUTHERN PLAINS THAT WILL EVENTUALLY TRACK FROM THE PANHANDLE OF OKLAHOMA NORTHEASTWARD INTO CENTRAL INDIANA BY FRIDAY MORNING. LIGHT SNOW WILL LIKELY START UP ON THURSDAY AFTERNOON ACROSS NORTHERN ILLINOIS ALONG THE LEADING EDGE OF THE WARM AIR ADVECTION OUT AHEAD OF THE SYSTEM. ONLY SOME LIGHT ACCUMULATIONS WILL COME OUT OF THIS INITIAL SNOW WITH THE HEAVIER AMOUNTS COMING IN THE EVENING THURSDAY INTO FRIDAY MORNING. FORECAST SOUNDINGS SHOW THE PROFILE SATURATING OUT FROM 20KFT ON DOWN TO THE SFC WHICH WILL LEAD TO SOME FAIRLY STRONG DENDRITIC GROWTH...PARTICULARLY FROM 6Z THRU 12Z. VERTICAL MOTIONS LOOK FAIRLY DECENT TO WHERE THERE COULD BE SOME PERIODS WHERE AROUND A HALF INCH TO AN INCH OF SNOW FALL PER HOUR. THE MAIN TRACK OF THE HEAVIEST SNOW WILL LIKELY BE ACROSS EAST CENTRAL ILLINOIS ON UP TOWARD SOUTHERN LAKE MICHIGAN WITH SNOW TOTALS AROUND 6 TO 9 INCHES ALONG THIS STRETCH. DUE TO THE TRACK OF THIS LOW GOING MORE SOUTH TO NORTH AND THE HEAVIEST BAND SHIFTING THAT WAY...HAVE ADDED A FEW COUNTIES TO THE WINTER STORM WATCH INCLUDING COOK/DU PAGE/WILL/GRUNDY COUNTIES. ALSO ADDED LAKE COUNTY ILLINOIS TO THE WATCH DUE TO A FAVORABLE LOW LEVEL WIND PROFILE THAT MAY LEAD TO SOME LAKE ENHANCEMENT TO THE SNOW IN THIS COUNTY. EVENTUAL TRANSITION OF WINTER STORM HEADLINES WILL LIKELY GO TO A WINTER STORM WARNING FOR THE COUNTIES CURRENTLY IN THE WATCH WITH A SNOW ADVISORY LIKELY BEING ADDED TO A FEW COUNTIES NORTH OF THE CURRENT WATCH FOR WHERE SNOW AMOUNTS OF AROUND 4 INCHES WILL BE EXPECTED. AFTER THIS STORM RAPIDLY MOVES OFF TO THE EASTERN GREAT LAKES AND THE NORTHEAST US...A RIDGE OF HIGH PRESSURE WILL MOVE IN ACROSS THE REGION INTO EARLY SATURDAY. A QUICK MOVING LOW WILL SKIRT OFF TO THE NORTH OF ILLINOIS ON SATURDAY LEAVING US ON THE DRY SIDE. THE NEXT SHOT FOR PRECIP WILL COME IN ON MONDAY AS THE NEXT STORM SYSTEM RAMPS UP ACROSS THE CENTRAL PLAINS. FIRST SHOT COMES THROUGH EARLY MONDAY WITH IT MORE LIKELY COMING DOWN AS RAIN WITH THE LOWER QUARTER OF THE TEMPERATURE PROFILE QUICKLY WARMING TO ABOVE FREEZING...BUT THERE COULD BE A BRIEF PERIOD WITH EITHER SOME SNOW OR A MIX WITH SLEET OR FREEZING RAIN BUT AT THIS POINT IT IS TOO FAR OUT TO START PINNING DOWN THOSE DETAILS. FRONTAL BOUNDARY STALLS OUT ACROSS THE OHIO RIVER VALLEY AND THINGS START TO GET INTERESTING TOWARD 00Z WEDNESDAY WHEN A SYSTEM TRACKS THROUGH CENTRAL ILLINOIS WITH SOME FAIRLY MEANINGFUL QPF ASSOCIATED WITH IT. WILL HAVE TO MONITOR THE FORECAST SEEING AS HOW THIS IT AT THE END OF THE FORECAST PERIOD...BUT THIS COULD SHAPE UP TO BE OUR NEXT BIG SNOW STORM AFTER OUR MAIN SHOW THURSDAY NIGHT INTO FRIDAY. TEMPERATURES THROUGHOUT THE PERIOD WILL START CLIMBING UP TOWARD SEASONAL READINGS TOMORROW AND REMAIN AT OR ABOVE NORMAL THROUGH THE EXTENDED PERIOD UNTIL THE VERY END WHEN COLDER AIR STARTS TO GET PULLED IN ON THE BACKSIDE OF THE LOW TUESDAY NIGHT INTO WEDNESDAY MORNING. HALBACH && .AVIATION... 1118 PM CST PAIR OF PHASING SHORT WAVES CONTINUE TO MOVE EAST INTO THE REGION LATE THIS EVENING BUT MODELS DAMP THESE OUT OVERNIGHT SO ONLY EXPECT CONTINUED INVASION OF MAINLY HI AND MID CLOUDS ACROSS THE TERMINALS. ANOTHER SHORT WAVE LIFTING NORTHEAST FROM OK AND KS AHEAD OF THE UPPER LOW OVER THE EASTERN CO-NM BORDER. MODELS LIFT THIS WAVE TO MO OVERNIGHT AND TO IL BY AFTERNOON AS THE UPPER LOW CONTINUES TO DIG INTO THE SOUTHERN PLAINS. UVV DEPICTED ACROSS FAR SOUTHERN WI...NORTHERN IL...NORTHERN IN AND SOUTHWEST LOWER MI BY MODELS AS WELL AS LIGHT QPF DURING THU AFTERNOON AHEAD OF THE MAIN SYSTEM. AS COLUMN MOISTENS EXPECT AT LEAST AREAS OF -SN TO BREAK OUT IN THIS BROAD REGION OF ISENTROPIC LIFT BY LATER AFTERNOON BUT CONDITIONS ONLY DROPPING DOWN TO MVFR THRU 00Z. RAPID DETERIORATION EXPECTED DURING THU EVE AS DEEP STRONG UVV SPREADS OVER NORTHEAST IL AND NW IN. LATEST MODELS STILL DEPICT HEAVIEST SNOWBAND WILL ALIGN SW TO NE FROM E CENTRAL IL ACROSS N CENTRAL IN INTO SOUTHERN LOWER MI SO HAVE KEPT CONDITIONS ABOVE VLIFR. TRS && .MARINE... 330 AM CST HIGH PRESSURE RIDGE CONTINUES TO MOVE ACROSS SOUTHERN LAKE MICHIGAN THIS MORNING...AND WILL MOVE ACROSS THE REMAINDER OF THE LAKE DURING THE DAY ALLOWING WIND SPEEDS TO FURTHER DIMINISH. STILL A FEW GUSTS INTO THE 25 KNOT RANGE BEING REPORTED ON THE FAR NORTH END OF THE LAKE EARLY THIS MORNING...WITH AIR TEMPERATURES IN THE SINGLE DIGITS MAINTAINING FREEZING SPRAY THREAT FOR A FEW MORE HOURS UNTIL WINDS SUBSIDE THERE. THUS WILL CONTINUE HEAVY FREEZING SPRAY WARNING TO RUN ITS COURSE THROUGH 7 AM CST. RIDGE THEN LIFTS NORTHEAST OF THE LAKE TONIGHT...AS LOW PRESSURE DEVELOPS OVER LOWER MISSISSIPPI VALLEY AND DEEPENS AS IT LIFTS NORTHEAST INTO OHIO VALLEY OVERNIGHT. THIS WILL TIGHTEN GRADIENT AGAIN TONIGHT...ESPECIALLY ON SOUTHERN HALF OF THE LAKE...WITH WINDS EXPECTED TO INCREASE TO 30 KNOTS TONIGHT THROUGH FRIDAY MORNING. SURFACE LOW PASSES OFF TO THE EAST OF THE LAKE BY LATE FRIDAY...AS WEAK HIGH PRESSURE RIDGE MOVES IN FROM THE WEST ALLOWING WINDS TO QUICKLY SUBSIDE. ALTHOUGH ILLINOIS AND INDIANA NEARSHORE WATERS LARGELY ICE COVERED...VIA MODIS POLAR ORBITING SATELLITE IMAGES FROM WEDNESDAY AFTERNOON...WITH HOIST SMALL CRAFT ADVISORY FOR 20-30 KNOT WINDS 00Z-21Z FRIDAY. RATZER && .LOT WATCHES/WARNINGS/ADVISORIES... IL...SNOW ADVISORY FROM 6 PM THIS EVENING TO 9 AM CST FRIDAY FOR ILZ005-006-011-012-019-020. WINTER STORM WARNING FROM 6 PM THIS EVENING TO 6 PM CST FRIDAY FOR ILZ013-014-021>023-032-033-039. IN...WINTER STORM WARNING FROM 6 PM CST /7 PM EST/ THIS EVENING TO 6 PM CST /7 PM EST/ FRIDAY FOR INZ001-002-010-011-019. LM...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 3 PM CST FRIDAY FOR LMZ740>745. && $$ WFO LOT ----------------------------------------------------------------------
