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Weather Story NWS Chicago, IL |
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Occasional light rain showers will come to an end this morning as an upper level disturbance lifts north of the area. A warm front across central Illinois will lift northward today and reach far northern Illinois later this afternoon, although the front is expected to hang up closer to Lake Michigan due to the colder water temperatures. High temperatures will range from the lower to mid 60's far south...to the upper 40's across extreme northeast Illinois. A stronger upper level disturbance will take aim on the area on Thursday, bringing heavier rain and some embedded thunderstorms to the area.
000 FXUS63 KLOT 102142 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 342 PM CST WED MAR 10 2010 .DISCUSSION... 341 PM CST A DEVELOPING LOW PRESSURE SYSTEM OVER THE SOUTHERN PLAINS WILL SHAPE OUR WEATHER FOR THE REMAINDER OF THE WEEK. MAIN QUESTIONS ASSOCIATED WITH THIS SYSTEM INVOLVE ON AND OFF PRECIP CHANCES LINGERING INTO THE WEEKEND...PLUS THE EXTENT OF FOG THAT WILL DEVELOP IN THIS VERY MOIST AIRMASS. THE UPPER LEVEL TROUGH AND SFC LOW THAT BROUGHT SHOWERS TO THE AREA LAST NIGHT ARE WEAKENING AS THEY CONTINUE TO LIFT NORTH. A STRONGER UPPER LEVEL SHORTWAVE MOVING OUT OF THE SOUTHERN ROCKIES IS DEVELOPING A NEW SFC LOW OVER THE SOUTHERN PLAINS AND SUPPORTING AREAS OF SEVERE CONVECTION THIS AFTERNOON ACROSS THE NW GULF COAST. FOG IS EXPECTED TO DEVELOP IN AREAS ALONG THE WISCONSIN BORDER OVERNIGHT AND DROP VSBYS PRETTY LOW IN PLACES...BUT HAVE COORDINATED WITH THE SWING SHIFT TO HAVE THEM HANDLE ANY NECESSARY HEADLINES THIS EVENING AFTER WE SEE HOW TRENDS ARE EVOLVING. GIVEN THE DECENT HEATING ACROSS MUCH OF THE AREA TODAY...WOULD EXPECT PROBLEMS TO BE LIMITED TO OUR NRN MOST COUNTIES. THE DEVELOPING LOW IS FCST TO LIFT NORTH THROUGH THE MISSOURI VALLEY AND BRING ADDITIONAL SHOWERS AND POSSIBLY SOME THUNDERSTORMS TO NRN ILLINOIS AND INDIANA TOMORROW. AM THINKING THAT LOW CAPE VALUES AND RELATIVELY WEAK SHEAR WILL LIMIT THE SEVERE POTENTIAL FOR US TOMORROW AS THIS SYSTEM OCCLUDES AND KEEPS THE MOST UNSTABLE AIR TO OUR SOUTH. THIS LARGE LOW PRESSURE SYSTEM BEGINS TO GET CUT OFF FROM THE NORTHERN FLOW AND TO SLOWLY WEAKEN AFTER TOMORROW...BUT LINGERS LONG ENOUGH OVER OUR AREA TO BRING AN EXTENDED PERIOD OF INCREASED PRECIP CHANCES. BY LATE SATURDAY INTO SUNDAY IT FINALLY MOVES INTO THE MID-ATLANTIC AHEAD OF A HIGH PRESSURE RIDGE DEVELOPING OVER THE NORTHERN PLAINS. THE NORTHERLY FLOW BETWEEN THESE TWO SYSTEMS EFFECTIVELY CUTS OFF GULF MOISTURE...SO POPS ARE PRETTY LOW FOR THE EARLY PART OF NEXT WEEK. LENNING && .AVIATION... 1800 UTC TAFS...SFC WARM FRONT EXTENDS FROM NR DBQ-DKB-JOT-VPZ AT 18Z. THIS BOUNDARY WILL CONTINUE TO LIFT NWD ACROSS NRN IL EARLY THIS AFTN...RESULTING IN IMPROVEMENT TO MVFR BKN CIGS AND VFR VIS OVR ENTIRE AREA BY 19-20Z. LOW PRESSURE CENTER NUMBER 1...NOW LOCATED ALONG THE IA/MN BORDER JUST E OF KFRM WILL CONTINUE TO ENTRAIN DRIER LLVL AIR INTO ITS WEAKENING CIRCULATION FROM WRN IL AND THE MID MS VLY. THIS SUPPORTS GUIDANCE WHICH SUGGESTS VFR CONDITIONS OVERSPREADING NRN IL AND NWRN INDIANA FROM SW-NE BY LATE THIS AFTN. SOME CONCERN THAT ISOL SHALLOW TOPPED SHOWERS MAY YET DVLP OVER EXTRM NRN IL ALONG WARM FRONT AS AIR MASS IMMEDIATELY UPSTREAM IS BECOMING A BIT UNSTABLE AND LATEST VIS IMAGERY IS SHOWING SLOWLY BUILDING CU FIELD OVER AREA. HAVE DECIDED TO LEAVE ANY PRECIP MENTION OUT OF 18Z TAFS THOUGH AS SHOWERS WILL BE WIDELY SCT AND VERY BRIEF. EXPECT VFR CONDITIONS TO PERSIST INTO THE EARLY EVENING HRS. AFTER AROUND 03Z HOWEVER...INDUCED WEAK RIDGING BETWEEN DECAYING LOW OVR IA...AND DEEPENING LOW NUMBER 2 NOW ORGANIZING OVER NERN OK...IS FCST TO PASS ACROSS REGION. THIS WILL CAUSE SFC AND LLVL FLOW TO BACK INTO ESE AS CIRCULATION ASSD WITH THIS SECOND LOW DEVELOPS NEWD OVER IL AND INDIANA. THIS IS EXPECTED TO QUICKLY RESULT IN RE DEVELOPMENT OF FOG AND LOW STRATUS DECK...WITH MOST TERMINALS LOWERING TO IFR OR LIFR CIGS/VIS AGAIN AFTER 06Z. THESE LOW CONDITIONS WILL THEN PERSIST INTO EARLY THURSDAY WHEN WIDESPREAD RAIN IS EXPECTED TO OVERSPREAD AREA FROM S-N. THIS PRECIPITATION SHOULD ERODE OR SCAVENGE FOG AND VERY LOW CIGS LEAVING GENERALLY MVFR CIGS. MERZLOCK && .MARINE... 1206 PM CST A LOW PRESSURE OVER FAR NORTH CENTRAL IOWA WILL WEAKEN AS IT LIFTS INTO SOUTHWEST MINNESOTA BY THIS EVENING. MEANWHILE...ANOTHER LOW OVER NORTH TEXAS WILL INTENSIFY AND MOVE TO NORTHERN MISSOURI BY THURSDAY MORNING. THIS LOW WILL THEN ALSO LIFT NORTH INTO IOWA ON THURSDAY WHILE IT TOO BEGINS TO SLOWLY FILL. THIS LOW WILL THEN CONTINUE TO WEAKEN AS IT DRIFTS SOUTHEAST ACROSS ILLINOIS FRIDAY AND INTO THE OHIO VALLEY ON SUNDAY. THIS WILL ALLOW SOUTHEAST TO EAST WINDS ACROSS THE WESTERN GREAT LAKES TO GRADUALLY BACK INTO THE NORTHEAST AND NORTH FRIDAY AND FRIDAY NIGHT. MERZLOCK && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$