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000 FXUS63 KLOT 101152 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 652 AM CDT SUN MAY 10 2009 .DISCUSSION... 344 AM CDT SCATTERED LIGHT SHOWERS MAY OCCUR TODAY AND THUNDERSTORMS ARE LIKELY WEDNESDAY. THE HIGH TEMPERATURE WILL CLIMB INTO THE 70S WEDNESDAY AND SATURDAY. TODAY...A SHORT WAVE TROUGH WAS OVER NORTH DAKOTA IN THE 500 MB HEIGHT FIELD THIS MORNING. THIS TROUGH WILL MOVE THROUGH WISCONSIN TODAY. ANOTHER WAVE WAS SEEN MOVING INTO NEBRASKA EARLY THIS MORNING. THIS WAS SEEN ON THE SATELLITE IR IMAGERY. THIS WAVE MAY BRING CLOUDS INTO NORTHERN ILLINOIS THIS AFTERNOON. THE 500 MB ANALYSIS AT 00 UTC SHOWS VERY COLD AIR MOVING INTO NORTHERN ILLINOIS AND NORTHERN INDIANA. THE COLD AIR ALOFT WILL CREATE SOME VERY STEEP LAPSE RATES THIS MORNING WHEN THE SUN IS HEATING THE GROUND. THE NAM MODEL AND LOCAL WRF MODEL SHOW THIS INSTABILITY IN THEIR BUFKIT FORECAST SOUNDINGS. A 3 KM WRF MODEL AND OUR LOCAL WRF SHOWS SCATTERED SMALL AMOUNTS OF PRECIPITATION ACCUMULATING THIS AFTERNOON. THE AMOUNTS ARE VERY LOW. THE LOW DEW POINTS WILL PREVENT A LOT OF SHOWERS OR HEAVY RAIN. WE ARE FORECASTING SCATTERED VERY LIGHT SHOWERS THIS MORNING AND ISOLATED SHOWERS THIS AFTERNOON. THE HIGH WILL SETTLE OVER MISSOURI AND ILLINOIS TONIGHT. THE COLDEST AIR WILL BE OVER NORTHERN ILLINOIS TONIGHT AND MONDAY MORNING. SOME LOW TEMPERATURES MAY REACH A LITTLE BELOW 38 DEGREES FAHRENHEIT. WILL ADD SOME PATCHY FROST FOR THE NORTHERN COUNTIES...AROUND THE AURORA VALLEY AND IN EASTERN PORTER COUNTY FOR TONIGHT. MONDAY THROUGH TUESDAY...A LARGE HIGH MOVES ACROSS ILLINOIS AND INDIANA MONDAY AND MONDAY NIGHT. THE SURFACE WIND WILL BECOME SOUTH BY TUESDAY MORNING. THE 850 MB FORECAST FROM THE GFS SHOWS AN INCREASING SOUTH WIND AND WARM AIR ADVECTION. THE HIGH TEMPERATURES WILL BE IN THE UPPER 60S TO LOWER 70S TUESDAY. THE 850 MB WIND ARE FORECAST TO INCREASE TO 40 KNOTS LATE TUESDAY NIGHT. THERE IS FORECAST A LARGE INCREASE IN MOISTURE TRANSPORT FROM THE SOUTH. THE SURFACE TO 850 MB SHEAR IS FORECAST TO INCREASE AS WELL. WE WILL ADD A CHANCE OF THUNDERSTORMS TUESDAY NIGHT. THIS IS AHEAD OF A STRONG COLD FRONT THAT WILL APPROACH ILLINOIS TUESDAY NIGHT. WEDNESDAY THROUGH SATURDAY...A STRONG COLD FRONT WILL MOVE THROUGH OUR FORECAST AREA WEDNESDAY. THE FORECAST HODOGRAPHS SHOW SOME SIGNIFICANT SHEAR OVER NORTHEAST ILLINOIS WEDNESDAY AFTERNOON. CAPE VALUES REACH 1350 J/KG AROUND FORD COUNTY. THERE WILL BE THUNDERSTORMS AND SOME OF THE THUNDERSTORMS MAY BE VERY STRONG SOUTH OF A LINE FROM HEBRON INDIANA TO STREATOR ILLINOIS. THIS IS ONLY AN OUTLOOK. A HIGH MOVES OVER ILLINOIS AND INDIANA THURSDAY AND FRIDAY. A WARM FRONT RETURNS FRIDAY. THE RETURNING WARM AIR AND INSTABILITY WILL GIVE A CHANCE OF THUNDERSTORMS FOR SATURDAY. THE HIGH TEMPERATURE WILL BE IN TH 60S THURSDAY AND FRIDAY AND IN THE 70S SATURDAY. && .AVIATION... 650 AM CDT 1200 UTC TAFS...MODELS SHOW MID LEVEL LOW CURRENTLY OVER THE MN-WI BORDER WEAKENING AS IT CONTINUES MOVING EAST SOUTHEASTWARD ACROSS WI AND LAKE MI TODAY...WITH AREA OF ISENTROPIC LIFT IN 050-100 LAYER AHEAD OF THE SHORT WAVE MOVING ACROSS SOUTHERN WI AND NORTHERN IL THIS MORNING AND EARLY AFTERNOON. EXPECT PATCHY CLOUDS IN THIS LAYER CURRENTLY JUST UPSTREAM ACROSS NORTHEAST IA...SOUTHERN WI AND SOUTHERN MN TO CONTINUE TO ADVANCE EAST SOUTHEASTWARD DURING THE MORNING THOUGH APPEARS BULK OF THESE MID CLOUDS WILL BE FROM FAR NORTHERN IL NORTHWARD. WEAK SURFACE LOW REFLECTION OF THE MID LEVEL LOW IS LOCATED IN CENTRAL WI AND PROGGED TO BECOME EVEN MORE ILL-DEFINED WITH TIME TODAY AS SHORT WAVE TROUGH WEAKENS AS IT MOVES ACROSS WI. MODELS DO INDICATE A SURFACE TROUGH/COLD FRONT DROPPING SOUTH THROUGH NORTHERN IL DURING THE AFTERNOON AS THE SHORT WAVE CONTINUES PAST THE TERMINALS AND OUT OVER SOUTHERN LAKE MI. THIS WILL SHIFT SYNOPTIC LOW LEVEL FLOW TO NORTHWESTERLY...WITH DIRECTION VEERING AROUND TO NORTH-NORTHEAST AND NORTHEASTERLY FOR THE CHI AREA TERMINALS DUE TO WEAK GRADIENT AND LAND/LAKE DIFFERENTIAL HEATING. HEATING WILL WARM SURFACE TO CONVECTIVE TEMPERATURE OF AROUND 15C WITH HIGHER BASED CU DEVELOPING MIDDAY AS A RESULT. THIS WILL BE UNDER THE NORTHERN FRINGE OF CIRRUS DECK CURRENTLY STREAMING FROM THE CENTRAL PLAINS TOWARD THE MID MS VALLEY. CU TO DISSIPATE WITH SUNDOWN AND EDGE OF HIGH CLOUDS TO SHIFT SOUTH OF THE LOCAL TERMINALS EARLY EVENING AS UPPER SPEED MAX DIGGING SOUTHEAST FROM OVER SLC REACHES THE LOWER MO VALLEY BY LATE THIS EVENING. WEAK PRESSURE GRADIENT OVER AREA WILL RESULT IN LIGHT OR NIL WIND AFTER SUNSET AND SURFACE DECOUPLES. TRS && .MARINE... 243 AM CDT LIGHT WINDS TODAY AND TONIGHT AS WEAK LOW PRESSURE FILLS AS IT MOVES SOUTHEASTWARD ACROSS WI TODAY...AND AS HIGH PRESSURE CENTERED OVER SOUTH CENTRAL CANADA SETTLES SOUTHEASTWARD ACROSS THE DAKOTAS AND UPPER MIDWEST TODAY AND THE MS VALLEY AND WESTERN GREAT LAKES TONIGHT. THE AREA OF HIGH PRESSURE SHIFTS EASTWARD ACROSS THE GREAT LAKES AND OHIO VALLEY MONDAY NIGHT. WINDS BECOME SOUTHEASTERLY AND INCREASE MONDAY NIGHT AND TUESDAY AS LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIE. AS THE LOW CONTINUES ON INTO ONTARIO DURING WEDNESDAY A TRAILING COLD FRONT WILL PUSH EAST THROUGH THE WESTERN GREAT LAKES VEERING WINDS ON LAKE MI FROM SOUTHEAST TO SOUTH THEN TO SOUTHWEST WITH THE PASSAGE OF THE COLD FRONT LATE IN THE DAY. TRS && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$
