Area Forecast Discussion
Issued by NWS Chicago, IL

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000 FXUS63 KLOT 252342 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 542 PM CST TUE NOV 25 2014 .SHORT TERM... 231 PM CST TONIGHT THROUGH WEDNESDAY... TEMPERATURE INVERSION HAS BEEN ABLE TO HOLD ONTO THE CLOUDS...WITH A STUBBORN STRATUS LAYER. FORTUNATELY THIS WEDGE OF CLOUDS WAS SLOWLY SLIDING EAST THIS AFTERNOON...WITH SOME CLEARING TAKING PLACE ACROSS WESTERN IL AND STRETCHING FURTHER WEST. SFC RIDGE WAS PUSHING EAST INTO SOUTHERN MO/NORTHERN AR...WHICH PLACED THE FORECAST AREA IN THE WESTERLY FLOW AT THE SFC. THERE IS SOME POTENTIAL THAT PATCHY FOG MAY DEVELOP TONIGHT...GIVEN THE SLOWLY ERODING CLOUD COVER AND DEW POINTS NOT ABLE TO DRY THIS AFTN. THIS CURRENTLY IS A LOW CONFIDENCE SCENARIO...BUT FELT IT WAS WORTH MENTIONING. WITH SOME CLEARING LIKELY TO TAKE PLACE IN THE WESTERN CWFA...TEMPS SHUD LIKELY BE ABLE TO RADIATE INTO THE LOW TEENS THERE. ELSEWHERE OVERNIGHT LOWS WILL HOVER ARND 18-22. SFC RIDGE FOR WED WILL STRETCH FROM THE WESTERN GULF NORTH INTO LOWER MICHIGAN...AND LIKELY BE SLOW TO DEPART THE REGION. THIS HAS BEEN IMPACTING THE PLACEMENT/MOISTURE WITHIN A WEAK SHORTWAVE DIVING SOUTHEAST ACROSS THE UPPER MIDWEST FOR WED. GUIDANCE HAS CONTINUED TO DEMONSTRATE LESS FAVORABLE SETUP FOR LGT SNOW AND ALSO TIMING FOR LATER WED. HI-RES LOCAL SOLUTION EVEN SUGGESTS FLURRIES LATE WED AFTN MAY BE THE EXTENT OF ANY PRECIP. WITH AT LEAST SOME HIGH/MID-LVL CLOUDS...TEMPS MAY AGAIN BE A CHALLENGE. CURRENT SOLUTIONS POINT TOWARDS HIGHS WARMING INTO THE LOW/MID 30S...BUT COULD SEE TEMPS STRUGGLING TO WARM BEYOND THE LOW 30S. WITH THE MID-LVL TROUGH AXIS PIVOTING EAST ACROSS THE FORECAST AREA WED EVE AND SOME WEAK OMEGA INTO THE MOIST LAYER...SOME LIGHT SNOW COULD PRODUCE A DUSTING WED EVE BUT THE CONFIDENCE WITH THIS SCENARIO CONTINUES TO DIMINISH. A FRONTAL BOUNDARY WILL THEN SLIDE EAST ACROSS THE REGION WED NGT...WITH ANOTHER RIDGE OF HIGH PRESSURE SLOWLY BUILDING IN FROM THE UPPER MIDWEST. BEACHLER && .LONG TERM... 231 PM CST THANKSGIVING THROUGH TUESDAY... 500MB TROUGH WILL BE DEPARTING THE REGION FOR THANKSGIVING...WITH BROAD SFC RIDGE BUILDING IN FROM THE WEST DURING THE DAY. THIS SHUD PROVIDE A GRADUAL EROSION TO THE CLOUD COVER. TEMPS WILL HOVER IN THE MID/UPR 20S...BUT IF CLOUDS CAN ERODE EARLIER THEN TEMPS MAY BE ABLE TO WARM A DEGREE OR TWO HIGHER. MID-LVL FLOW BEGINS TO TRANSITION INTO A SEMI-ZONAL SETUP...WITH THE POTENTIAL FOR ANOTHER LOW PRESSURE SYSTEM BRINGING A CHC FOR LGT SNOW FRI. ENSEMBLES CONTINUE TO SUGGEST THAT SAT COULD WARM WELL INTO THE 40S...PERHAPS TOUCHING 50 DEGREES IN THE SOUTHERN CWFA. FOR THE SECOND HALF OF THE WEEKEND GUIDANCE DIFFERS ON TIMING OF A FRONTAL BOUNDARY. IF A SLOWER SOLUTIONS OCCURS...SUN COULD ALSO BE A MILD DAY WITH HIGHS IN THE MID/UPR 40S. GUIDANCE HAS BEEN SUGGESTING A NARROW BAROCLINIC ZONE MAY DEVELOP ALONG THE OHIO VALLEY EARLY NEXT WEEK...WHICH COULD KEEP SOME LGT PRECIP IN THE SOUTHEAST FORECAST AREA. BEACHLER && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 00Z... * BRIEF PERIOD OF MVFR CIGS 1600-2000 FT POSSIBLE EARLY THIS EVENING. RATZER //DISCUSSION...UPDATED 00Z... WEAK SURFACE HIGH PRESSURE DRIFTING EAST ACROSS ILLINOIS AND WESTERN INDIANA THIS EVENING. WEST WINDS 5-10 KT EARLY WILL DIMINISH TO 5 KT OR LESS OVERNIGHT...GRADUALLY BACKING SOUTHWEST THIS EVENING AND EVENTUALLY TO SOUTHEAST EARLY WEDNESDAY IN RESPONSE TO AN AREA OF LOW PRESSURE WHICH WILL MOVE FROM THE DAKOTAS TO THE LOWER OHIO VALLEY. WINDS...WHICH SHOULD REMAIN LESS THAN 10 KT THROUGH WEDNESDAY...WILL THEN SHIFT NORTHERLY WEDNESDAY EVENING. CHICAGO TERMINALS HAVE BEEN WITHIN WESTERN PERIPHERY OF LOW LEVEL MOISTURE TRAPPED BENEATH AN INVERSION BASED AROUND 2500 FT AGL... WITH MVFR STRATOCU DECK IN THE 1600-2000 FT RANGE LINGERING MAINLY SOUTH/EAST OF ORD. THIS DECK WILL CONTINUE TO DRIFT SLOWLY EAST THIS EVENING MAINLY AFFECTING MDW/GYY THROUGH THE EARLY EVENING HOURS. EROSION OF THIS DECK AS OCCURRED FARTHER NORTH ACROSS DPA- ORD SO NOT EXPECTING A CEILING AT THIS TIME. WITH LIGHT WIND REGIME THERE IS A LOW-PROBABILITY POTENTIAL FOR SOME MVFR SHALLOW FOG TO DEVELOP MAINLY AWAY FROM CHICAGO METRO TERMINALS LATE TONIGHT...THOUGH CONFIDENCE IS LOW EN0UGH TO LEAVE OUT OF TAFS AT DPA AND RFD AT THIS TIME. VFR CONDITIONS EXPECTED OVERNIGHT AND WEDNESDAY...WITH ONLY MID/HIGH CLOUDS ASSOCIATED WITH DISTURBANCE PASSING TO THE SOUTHWEST OF THE FORECAST AREA. RATZER //ORD AND MDW CONFIDENCE...UPDATED 00Z... * MEDIUM-HIGH CONFIDENCE IN NO PERSISTENT MVFR CIG THIS EVE. * HIGH CONFIDENCE ALL OTHER ELEMENTS. RATZER //OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z... THURSDAY...SLGT CHANCE OF MVFR LGT SNOW EARLY...OTHERWISE VFR. FRIDAY...SLGT CHANCE OF LGT SNOW. MVFR POSSIBLE. SATURDAY THROUGH MONDAY...PRIMARILY VFR...THOUGH A PERIOD OF MVFR OR IFR CIGS POSSIBLE SATAURDAY INTO EARLY SUNDAY. RATZER && .MARINE... 147 PM CST A HIGH PRESSURE RIDGE CONTINUES TO PUSH EAST CAUSING WINDS TO DIMINISH ACROSS THE REGION. MEANWHILE A LOW CURRENTLY OVER THE DAKOTAS REACHES THE MID MISSISSIPPI VALLEY TOMORROW MORNING. LIGHT WINDS BECOME EAST OVER THE SOUTHERN HALF OF THE LAKE AND VARIABLE OVER THE NORTHERN HALF TOMORROW AFTERNOON. THE LOW WEAKENS AS IT PASSES OVER CENTRAL IL TOMORROW AND HIGH PRESSURE THEN BUILDS OVER THE PLAINS TOMORROW NIGHT. NORTH TO NORTHWEST WINDS INCREASE TO 30 KT THURSDAY AS THE PRESSURE GRADIENT INCREASES BETWEEN THE HIGH OVER THE PLAINS AND LARGE LOW MOVING UP THE EAST COAST. WINDS DIMINISH AS THE HIGH MOVES OVER THE LAKE THURSDAY NIGHT. WINDS THEN BECOME SOUTH BEHIND THE HIGH FRIDAY. GUIDANCE DIFFERS ON HOW QUICKLY THE NEXT LOW MOVES OVER LAKE SUPERIOR...BUT THE PRESSURE GRADIENT INCREASES AHEAD OF THE LOW RESULTING IN SOUTH WINDS AROUND 30 KT LATE THIS WEEK. HAVE THE WINDS FORECASTED TO COME UP FRIDAY AFTERNOON...BUT THEY COULD COME UP AS LATE AS SATURDAY MORNING. 20 KT WINDS PERSIST THROUGH THE WEEKEND WITH SOUTHWEST WINDS BECOMING NORTH SUNDAY AFTERNOON. ANOTHER HIGH PRESSURE SYSTEM MOVES OVER THE LAKE EARLY NEXT WEEK WITH STRONG SOUTH WINDS BEHIND IT. JEE && .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/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO

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