Area Forecast Discussion
Issued by NWS Chicago, IL

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000 FXUS63 KLOT 021135 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 635 AM CDT WED SEP 2 2015 .SHORT TERM... 328 AM CDT THROUGH THURSDAY... PRIMARY CONCERN IN THE NEAR TERM IS CONVECTIVE POTENTIAL TONIGHT. ANOTHER VERY WARM TO ALMOST HOT DAY EXPECTED TODAY WITH HIGHS ONCE AGAIN MAKING A RUN AT 90 DEGREES AND PROBABLY ECLIPSING 90 IN MANY AREAS. SOME DEBRIS CLOUDINESS FROM IOWA CONVECTION COULD FILTER SUN A BIT IN OUR WESTERN CWA AND PERHAPS KEEP TEMPS A DEGREE OR TWO COOLER...BUT WITH CONVECTION LIKELY TO WEAKEN NOT ANTICIPATING A BIG IMPACT. WELL DEFINED SHORTWAVE ON WATER VAPOR IMAGERY OVER MINNESOTA AND WESTERN IOWA WILL CONTINUE TO SLOWLY PROGRESS EASTWARD THROUGH TONIGHT. BRUNT OF THE CONVECTION IS EXPECTED TO REMAIN TO OUR NORTH OVER WISCONSIN TONIGHT...BUT GLANCING BLOW FROM SOUTHERN EXTENT OF THE SHORTWAVE SHOULD RESULT IN SOME WEAK HEIGHT FALLS AND PERHAPS ENOUGH FORCING TO SUPPORT SOME CONVECTION IN OUR CWA. VARIOUS CONVECTIVE ALLOWING ENSEMBLES ARE NOT OVERLY AGGRESSIVE WITH CONVECTIVE CHANCES TONIGHT...SO LARGELY MAINTAINED PREVIOUS POPS WITH JUST SMALL CHANCES OVER MAINLY NORTHERN CWA CLOSER TO THE TRACK OF THE STRONGEST PORTION OF THE VORT. A PORTION OF THIS VORT COULD BEGIN TO TURN SOUTHEAST AS IT REACHES THE EASTERN EXTENT OF THE UPPER RIDGE...LINGERING IN THE AREA THURSDAY. COMBINATION OF LOWER HEIGHTS AND POTENTIAL FOR LOW LEVEL CONVERGENCE ALONG OUTFLOW AND/OR LAKE BREEZE SUGGESTS IT WOULD BE PRUDENT TO ADD SOME LOW CHANCE POPS FOR THURSDAY AS WELL. ASSUMING CONVECTION AND/OR CONVECTIVE DEBRIS AREN`T TERRIBLY PROMINENT THEN THURSDAY WILL BE ANOTHER DAY WITH TEMPS MAKING A RUN AT 90 DEGREES. MUCH OF AVAILABLE GUIDANCE SUGGESTS A LAKE BREEZE COULD FORM IN THE AFTERNOON...WHICH IF IT MATERIALIZES WOULD CAUSE LAKE ADJACENT AREAS TO SEE TEMPS DROP OFF A BIT IN THE AFTERNOON. IZZI && .LONG TERM... 338 AM CDT THURSDAY NIGHT THROUGH TUESDAY... CONTINUED UNSEASONABLY WARM AND HUMID CONDITIONS FRIDAY ALONG WITH SLIGHTLY LOWER HEIGHTS WITHIN A BREAK IN THE UPPER RIDGE OVER THE REGION ARGUES FOR SOME MORE SLIGHT CHANCE POPS FOR FRIDAY AS WELL WITH LAKE BREEZE ONCE AGAIN A CANDIDATE TO FOCUS DEVELOPMENT. HEADING INTO THE WEEKEND GFS AND ECMWF VARY ON LOW LEVEL WIND FLOW AND POTENTIAL FOR LAKE BREEZES. ECMWF WOULD SUGGEST LITTLE OR NO LAKE BREEZE WHILE GFS MORE PROMINENTLY DEVELOPS HEALTHY LAKE BREEZES BOTH DAYS. AWAY FROM THE LAKE THE FORECAST IS MORE STRAIGHT FORWARD...JUST CONTINUED UNSEASONABLY WARM AND RATHER HUMID. IF GFS ADVERTISED LAKE BREEZE MATERIALIZES THEN TEMPS WOULD LIKELY HOLD IN THE 70S ALONG THE SHORE OVER THE WEEKEND...WHILE ECMWF WOULD SUGGEST THE UPPER 80S/NEAR 90 DEGREE HEAT WOULD MAKE IT RIGHT UP TO THE SHORELINE. MONDAY COULD BE ONE OF THE HOTTEST DAYS OF THE NEXT SEVEN DEPENDING ON DEBRIS CLOUDS AND TIMING OF THE FRONT. FOR NOW KEPT HIGHS IN THE UPPER 80S/NEAR 90...BUT WITH SUNSHINE AND CURRENT TIMING OF FRONT PANNING OUT HIGHS COULD REACH LOW/MID 90S. COLD FRONT LOOKS TO APPROACH REGION LATE MONDAY AND COULD SLOW OR STALL OUT NEARBY MONDAY NIGHT INTO TUESDAY BRINGING A CONTINUED THREAT OF SHOWERS AND THUNDERSTORMS. IZZI && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 12Z... * CHANCE FOR TSRA LATE TONIGHT. RODRIGUEZ //DISCUSSION...UPDATED 12Z... VFR CONDITIONS WITH LIGHT SOUTHERLY WINDS IN PLACE THIS MORNING...LOOK TO CONTINUE TODAY INTO TONIGHT. AREA OF SHOWERS/THUNDERSTORMS SLOWLY MOVING EAST THROUGH IOWA THIS MORNING WILL DISSIPATE THIS MORNING...BUT WITH ASSOCIATED HIGH LEVEL CLOUD COVER LIKELY PUSHING EAST OVER THE TERMINALS. GUIDANCE VARIES WITH PRECIP POTENTIAL TODAY AND TONIGHT...BUT STILL THINK THE HIGHEST CHANCES FOR PRECIP WONT ARRIVE UNTIL LATER TONIGHT INTO THURSDAY MORNING. HAVE INTRODUCED TSRA INTO THE TAFS BUT DO HAVE LOWER CONFIDENCE AS TO EXACT TIMING AND DURATION...WHICH WILL LIKELY NEED REFINED WITH LATER FORECASTS. RODRIGUEZ //ORD AND MDW CONFIDENCE...UPDATED 12Z... * LOW MEDIUM CONFIDENCE IN TSRA POTENTIAL TONIGHT. * HIGH CONFIDENCE WITH WIND SPEED/DIRECTION. RODRIGUEZ //OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z... THURSDAY NIGHT...SLIGHT CHANCE OF TSRA. FRIDAY...SLIGHT CHANCE OF TSRA. SATURDAY...SLIGHT CHANCE OF TSRA. SUNDAY...VFR. MONDAY...CHANCE OF TSRA. TUESDAY...CHANCE OF TSRA. RODRIGUEZ && .MARINE... 429 AM CDT LARGE HIGH PRESSURE WILL CONTINUE TO DOMINATE THE EASTERN THIRD OF THE COUNTRY THIS WEEK WITH ANY ADDITIONAL LOW PRESSURE SYSTEMS STAYING NORTHWEST OF THE REGION. WHAT THIS WILL MEAN FOR THE LAKE IS GENERALLY LIGHTER WINDS THIS WEEK...WITH DIRECTIONS LIKELY VARYING FROM AN EASTERLY OR SOUTHERLY DIRECTION. FOG LIKELY OVER THE LAKE AGAIN THIS MORNING...BUT NOT AS DENSE AS THE LAST COUPLE OF DAYS. HOWEVER...PATCHY DENSE FOG WILL STILL BE POSSIBLE IN SOME LOCATIONS TODAY. RODRIGUEZ && .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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