Area Forecast Discussion
Issued by NWS Chicago, IL

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000 FXUS63 KLOT 180245 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 945 PM CDT THU APR 17 2014 .DISCUSSION... 309 PM CDT A RELATIVELY BENIGN WEATHER PERIOD IS IN STORE FOR THE NEXT FEW DAYS...WITH THE ONLY CHANCE OF ANY PRECIP THROUGH SUNDAY BEING TONIGHT. THE MAIN FORECAST CONCERNS OVER THE NEXT FEW DAYS WILL BE TEMPERATURES...AS THERE WILL LIKELY BE SOME DECENT TEMPERATURE GRADIENTS ACROSS THE AREA...DUE IN LARGE PART TO THE ONSHORE FLOW EXPECTED ACROSS NORTHEASTERN ILLINOIS ON FRIDAY AND SATURDAY. CURRENTLY THERE IS A GOOD AMOUNT OF MID AND HIGHER LEVEL CLOUDINESS STREAMING NORTHEASTWARD ACROSS THE AREA AHEAD OF A SHEARED OUT SHORT WAVE...CURRENTLY IN PLACE ACROSS THE MID AND LOWER MISSOURI VALLEY. MODEL GUIDANCE CONTINUES TO SPARK OFF AN AREA OF SHOWERS ACROSS PORTIONS OF THE REGION THIS EVENING AND OVERNIGHT AS THIS SHORT WAVE DISTURBANCE APPROACHES AND INDUCES SOME ISENTROPIC ASCENT ACROSS THE AREA. OVERALL...I FOLLOWED CLOSE TO THE INHERITED FORECAST...WHICH PLACES THE CHANCES FOR THIS ACTIVITY MAINLY FROM MID EVENING THROUGH LATE TONIGHT FOR AREAS ALONG AND SOUTH OF A LINE FROM CHICAGO TO MENDOTA. A 1030 MB SURFACE HIGH IS EXPECTED TO BUILD IN ACROSS THE UPPER GREAT LAKES REGION ON FRIDAY. THIS WILL SET UP A NORTH-NORTHEASTERLY ONSHORE FLOW ACROSS THE AREA DURING THE DAY. AS SUCH...EXPECT CHILLY CONDITIONS ON FRIDAY ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA...WHERE A ENHANCED LAKE BREEZE WILL LIKELY KEEP TEMPERATURES IN THE 40S FORE AREAS NEAR THE LAKE. FARTHER INLAND...HOWEVER...TEMPERATURES SHOULD WARM INTO THE 50S...WITH EVEN SOME LOW 60S POSSIBLE WELL INLAND. TEMPERATURES BEGIN TO MODERATE AREA-WIDE ON SATURDAY AS THE LOWER LEVEL FLOW TURNS OUT OF THE SOUTHEAST IN RESPONSE TO LOW PRESSURE MOVING ACROSS THE NORTHERN PLAINS AND SOUTHERN CANADA. TEMPERATURES LOOK TO CLIMB INTO THE 60S FOR MOST AREAS...WITH THE EXCEPTION OF FAR NORTHEAST ILLINOIS...WHERE SOUTHEASTERLY ONSHORE FLOW LOOKS TO KEEP THINGS COOLER. SUNDAY DEFINITELY LOOKS TO BE THE BEST DAY OF THE WEEKEND. SOUTH-SOUTHWESTERLY FLOW IS EXPECTED TO TRANSPORT AN EVEN WARMER AIR MASS IN ACROSS THE AREA. MODEL GUIDANCE IS IN VERY GOOD AGREEMENT IN ADVECTING IN 15 (9) DEGREE CELSIUS 925 MB (850 MB) TEMPERATURES. LOCAL CLIMO FOR THESE VALUES THIS TIME OF YEAR INDICATE HIGH TEMPERATURES GETTING INTO THE LOW TO POSSIBLY MID 70S ACROSS THE AREA. THE NEXT CHANCE FOR PRECIPITATION LOOKS TO BE ON MONDAY AS ANOTHER WEAK FRONTAL SYSTEM AND MID LEVEL DISTURBANCE PUSHES ACROSS THE AREA. FOLLOWING IN THE WAKE OF THIS FRONTAL MONDAY...LOOKS TO BE ANOTHER DAY OR TWO PERIOD OF NORTHEASTERLY ONSHORE COOLING FLOW...WHICH WILL AGAIN COULD SET UP A DECENT THERMAL GRADIENT BETWEEN THE LAKE SHORE AND AREAS FARTHER INLAND. WAY OUT...TOWARDS THE END OF THE CURRENT FORECAST PERIOD...GUIDANCE IS IN GOOD AGREEMENT IN DEVELOPING A GOOD STORM SYSTEM ACROSS THE PLAINS..THEY JUST DIFFER SIGNIFICANTLY WITH THE TIMING. THIS SYSTEM LOOKS TO PRODUCE A PERIOD OF MUCH WARMER WEATHER AND ALSO ANOTHER THREAT FOR SHOWERS AND THUNDERSTORMS AT THE END OF THE PERIOD. KJB && .AVIATION...
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//ORD AND MDW CONCERNS...UPDATED 03Z... * WINDS SHIFTING FROM WSWLY TO NELY LATE EVENING. KREIN //DISCUSSION...UPDATED 00Z... THE LOW PRESSURE SYSTEM OVER NRN WISCONSIN IS WEAKENING RAPIDLY AS IT MOVES OVER NRN LAKE MICHIGAN EARLY THIS EVENING. AN ASSOCIATED WEAK COLD FRONT EXTENDS SWWD INTO SRN MO...BUT THE BOUNDARY IS VERY DIFFUSE OVER NRN IL. THROUGH THE EARLY EVENING...THE BOUNDARY IS EXPECTED TO WASH OUT AND THAT WINDS SHOULD TURN NELY AS EITHER A LATE LAKE BREEZE OR INVERTED TROUGH FORMS ALONG THE LAKEFRONT AND MOVES INLAND. THE LATEST RUNS OF THE HIGH RES SHORT RANGE MODEL GUIDANCE INDICATE THAT WINDS AT ORD/MDW/GYY COULD TURN NELY AS EARLY AS ARND 02Z. WINDS SHOULD THEN REMAIN GENERALLY NELY AT THE TERMINALS THROUGH THE REMAINDER OF THE FCST PERIOD AS HIGH PRESSURE BUILDS ACROSS THE UPPER MISSISSIPPI VALLEY AND ACROSS THE WESTERN GREAT LAKES REGIONS. A MID LEVEL DISTURBANCE TRACKING NEWD THROUGH THE MIDDLE MISSISSIPPI VALLEY COULD BRING SOME RAIN TO CNTRL IL AND NRN IN THIS EVENING...BUT ANTICIPATE THAT ANY PCPN SHOULD REMAIN SOUTH OF THE TERMINALS...BUT THERE IS A CHANCE THAT GYY COULD SEE SOME RAIN LATE THIS EVENING IF THE PCPN CAN OVERCOME THE LOW LEVEL DRY AIR AND REACH THE SFC. OTHERWISE...CONDITIONS AT THE TERMINALS SHOULD BE VFR/WX NIL THROUGH THE DAY TOMORROW. KREIN //ORD AND MDW CONFIDENCE...UPDATED 03Z... * MEDIUM CONFIDENCE IN TIMING OF WIND SHIFT...WITH HIGHER CONFIDENCE IN WIND TRENDS LATTE TONIGHT AND TOMORROW. * MEDIUM TO HIGH CONFIDENCE THAT ANY PCPN WILL REMAIN SOUTH OF THE TERMINALS. * HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS. KREIN //OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z... SATURDAY...VFR/WX NIL. SUNDAY...VFR/WX NIL. MONDAY...CHANCE RAIN WITH MVFR CIGS/VIS LIKELY. IFR CIGS POSSIBLE. TUESDAY...VFR/WX NIL. WEDNESDAY...CHANCE RAIN WITH MVFR CIGS/VIS LIKELY. IFR CIGS POSSIBLE. KREIN
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&& .MARINE... 216 PM CDT WEAKENING LOW PRESSURE OVER NORTHEAST WISCONSIN THIS AFTERNOON WILL CONTINUE TO LIFT NORTHEAST AND WEAKEN...REACHING NORTHEAST ONTARIO BY DAYBREAK FRIDAY. THIS LOW HAS A FRONTAL BOUNDARY THAT WILL CONTINUE TO SLIDE EAST ACROSS THE LAKE THIS AFTERNOON...WITH WINDS SLOWLY TURNING WESTERLY TO NORTHWESTERLY. THE GRADIENT WILL BE CONTINUE TO WEAKEN THIS EVENING...AS AN AREA OF HIGH PRESSURE LOCATED ACROSS CENTRAL CANADA WILL SLIDE EAST AND ELONGATE COVERING THE WESTERN GREAT LAKES REGION BY MIDDAY FRIDAY. THE NEXT WEATHER SYSTEM WILL BEGIN TO DEVELOP FRIDAY NIGHT ACROSS THE CENTRAL PLAINS...ALLOWING A TIGHTENING GRADIENT TO DEVELOP ACROSS THE SOUTHERN HALF OF THE LAKE EARLY SATURDAY. IT DOES NOT APPEAR AT THIS TIME ANY SUBSTANTIAL INCREASE IN THE WINDS WILL OCCUR. OTHERWISE THE NEXT CHANCE FOR MODERATE TO STRONG WINDS WILL BE FROM EARLY NEXT WEEK ON AS A STRONGER LOW PRESSURE SYSTEM COULD IMPACT THE REGION. BEACHLER && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO

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