Area Forecast Discussion
Issued by NWS Chicago, IL

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000 FXUS63 KLOT 260856 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 356 AM CDT TUE MAY 26 2015 .SHORT TERM... 319 AM CDT THROUGH TUESDAY NIGHT... FOR THE REMAINDER OF THE OVERNIGHT HOURS...CONDITIONS WILL REMAIN QUIET ACROSS THE CWA AS A SERIES OF SHORT WAVES CONTINUE TO TRACK NORTH AROUND THE TOP OF A PERSISTENT UPPER LEVEL RIDGE WHICH EXTENDS FROM THE SERN CONUS THROUGH THE UPPER MISSISSIPPI VALLEY. THIS UPPER RIDGE HAS BEEN THE FEATURE WHICH HAS CONTROLLED THE PATH OF THE SERIES OF SHORTWAVES LIFTING OUT OF THE SOUTHERN PLAINS...AND WILL CONTINUE TO DO SO THROUGH THE DAY TODAY. SLY...MODERATELY STRONG...WINDS WILL PERSIST THROUGH THE NIGHT...AND MUCH OF THE DAY ALLOWING FOR SFC DEWPOINTS TO REMAIN CONSISTENT OR POSSIBLE INCH A LITTLE HIGHER. MAIN CONCERN FOR THE MORNING HOURS WILL BE THE TRACK OF A STRONG SHORT WAVE AND ASSOCIATED SFC LOW LIFTING NORTHWARD THROUGH THE MIDDLE MISSISSIPPI VALLEY. THIS FEATURE WILL PREDOMINANTLY IMPACT ERN IOWA AND WRN IL BY ARND DAYBREAK. THROUGH THE MORNING...THE COMBINATION OF ISENTROPIC LIFT IN THE WARM SECTOR OF THE SYSTEM...ALL OF IL AND INTO NWRN IN...WILL LEAD TO SOME DESTABILIZATION ACROSS THE REGION. A SFC TROUGH...AS WELL INDICATED BY THE LATEST HIGH RES GUIDANCE...WITH LIFT THROUGH NRN IL/IN THROUGH THE DAY...COINCIDENT WITH A STRONG SSWLY LOW LEVEL JET OF 45- 50 KT...WITH PROVIDE THE POTENTIAL FOR SHOWERS AND STRONG TO SEVERE THUNDERSTORMS ACROSS THE CWA. BASED ON WIND PROFILES AND MID LEVEL DRYING...THE PRIMARY CONCERN WITH REGARD TO SEVERE WEATHER WILL BE STRONG WIND GUSTS. HOWEVER...SOME OF THE HIGH RES SFC WIND GUIDANCE SUGGEST SOME SLIGHT BACKING OF SFC WINDS FROM 180-190 DEGREES TO 160- 170 DEGREES...WHILE WINDS ALOFT REMAIN SWLY. THIS SLIGHT BACKING OF THE SFC WINDS COULD PROVIDE ENOUGH DIRECTIONAL SHEAR THROUGH THE LOWER LEVELS TO BRING AN ISOLD TORNADO THREAT. LOCALLY HEAVY RAINFALL WILL ALSO BE CONCERNED WITH PWATS REACHING 1.75 INCHES LATER THIS MORNING. HOWEVER...FLOODING WILL LIKELY NOT BE A SIGNIFICANT CONCERN AS THE SWLY WINDS RIGHT OFF THE DECK WILL RANGE FROM ARND 45 KT ABOVE THE BOUNDARY LAYER TO ARND 90KT AT UPPER LEVELS WHICH SHOULD ALLOW ANY OF THE STRONGER STORMS THAT DO DEVELOP TO MOVE QUICKLY. BY EARLY AFTERNOON...THE MAIN SHORT WAVE WILL LIFT INTO WISCONSIN WHILE A SFC TROUGH TRACKS EAST ACROSS THE AREA. THIS WILL LEAD TO WINDS AT THE SFC VEERING TO SWLY...SETTING UP A UNIDIRECTIONAL WIND PROFILE...EFFECTIVELY MINIMIZING THE SEVERE WEATHER THREAT TO THE REGION. BY LATE AFTERNOON AND INTO THE EVENING THE MODELS ARE ADVERTISING THAT A DRY SLOW SHOULD NOSE INTO NRN IL...EFFECTIVELY CUTTING OFF THE PCPN AREA INTO 2 SEPARATE AREA...ONE OVER WISCONSIN AND ERN IOWA AND ANOTHER MORE FOCUSED OVER INDIANA. THE NWRN INDIANA COUNTIES WILL STILL HAVE A CHANCE FOR SOME SHOWERS AND THUNDERSTORMS INTO THE EVENING...WHILE PCPN CHANCES OVER NRN IL BEGIN TO WANE. MUCH OF THE MODEL GUIDANCE ALSO INDICATED THAT THE SHORTWAVE SHOULD SLOW IT`S PROGRESSION THROUGH WISCONSIN AS IT APPROACHES THE APEX OF THE UPPER RIDGE. AN ASSOCIATED SFC TROUGH/COLD FRONT EXTENDING SOUTHWEST FROM THE SFC LOW WILL LINGER OVER ERN IOWA IN THE EARLY EVENING BEFORE STEADILY PUSHING ACROSS NRN IL AND INTO NWRN IN OVERNIGHT. THROUGH THE NIGHT...THE STRONGEST UPPER LEVEL FORCING WILL BE WELL NORTH OF THE CWA...SO ANY LINGERING CHANCES FOR PCPN OVERNIGHT WILL BE LOW AND LIKELY CONFINED TO THE NRN TIER COUNTIES OF IL...ALONG THE WI BORDER. KREIN && .LONG TERM... 229 AM CDT WEDNESDAY THROUGH MONDAY... WEDNESDAY THROUGH THURSDAY... OPEN 500MB WAVE WILL BE LIFTING NORTHEAST ACROSS THE UPPER MIDWEST INTO ONTARIO AND EVENTUALLY QUEBEC...WITH HEIGHTS SLOWLY INCREASING WED AFTN. SFC FEATURES REMAIN DISORGANIZED WED...WITH A BOUNDARY SLOWLY SHIFTING EAST. OPER GUIDANCE DIFFERS ON HOW QUICKLY PRECIP WILL DEPART THE REGION. ENSEMBLE DATA SUGGESTS HOLDING ONTO CHC TO SLIGHT CHC POPS MAINLY FOR THE CENTRAL/EASTERN CWFA WED/WED EVE. ALTHOUGH WITH SOME HINT OF SFC HEIGHTS NUDGING UP...IT IS POSSIBLE THAT SOME DRY AIR COULD FILTER IN AND KICK PRECIP EAST BY MIDDAY AND ALLOW FOR A MAINLY DRY WED. SFC WINDS WILL BE TURNING SOUTHWEST TO WEST...KEEPING AN OFFSHORE FLOW FOR LOCATIONS CLOSE TO LAKE MICHIGAN. TEMPS SHOULD YET AGAIN TOUCH UPR 70S TO ARND 80 WED...IF CLOUDS AND PRECIP CAN PUSH EAST BY MIDDAY...SOME CLEARING WOULD ALLOW SFC TEMPS TO PUSH A COUPLE DEGREES WARMER INTO THE LOW 80S IN SOME LOCATIONS. LATE IN THE EVENING THE GRADIENT SLACKENS FURTHER...AND COULD ALLOW A LATE DAY ONSHORE FLOW TO DEVELOP FOR AREAS ADJACENT TO LAKE MICHIGAN. MID-LVL FLOW BEGINS TO FLATTEN AS A WEAK SFC RIDGE BECOMES ORIENTED FROM WESTERN QUEBEC SOUTH THROUGH THE EASTERN OHIO RIVER VALLEY. THIS WILL GENERALLY ALLOW A SOUTHERLY FLOW...ALTHOUGH THE GRADIENT IS NOT VERY STRONG. THIS SHOULD SET THE STAGE FOR A LAKE BREEZE/ONSHORE FLOW TO DEVELOP THUR. TIMING COULD END UP BEING SLIGHTLY EARLIER GIVEN THE LIGHT SFC GRADIENT. GUIDANCE HAS BEEN CONSISTENT IN HOLDING PRECIP WEST/SOUTH OF THE FORECAST AREA THUR...AS A RESULT OF THE WEAK SFC RIDGING. SO ONE MORE MILD DAY WITH HIGHS WARMING BACK INTO THE UPR 70S/LOW 80S...HOWEVER AS PREVIOUSLY NOTED...A LAKE BREEZE IS LIKELY TO DEVELOP. THIS WILL BLEED THE MUCH COOLER MARINE AIR WEST ACROSS NORTHEAST IL AND DOWNTOWN CHICAGO. IF THE TIMING IS EARLIER IN THE DAY THUR...TEMPS MAY NOT WARM BEYONG THE LOW/MID 60S ALONG THE CHICAGO LAKEFRONT. FLOW THEN TURNS SOUTHERLY THUR NIGHT WITH THE MORE PROGRESSIVE FLOW IN THE MID-LVLS PUSHING THE RIDGING EAST. A RETURN FLOW MOISTURE WILL CONTINUE TO BE FOCUSED ACROSS THE CENTRAL CONUS THUR EVE...WITH A SLOW MOVING FRONTAL BOUNDARY NUDGING EAST THUR NIGHT TOWARDS WESTERN IL. THIS FRONTAL BOUNDARY WILL BECOME ENERGIZED AS A ROBUST 500MB VORT MAX BREAKS SOUTH FROM CENTRAL CANADA LATE THUR NIGHT. THIS SHOULD ALLOW FOR AN ATMOSPHERIC RIVER TO DEVELOP FROM THE SOUTHERN PLAINS STRETCHING NORTH THROUGH THE MID-MISSOURI VALLEY INTO THE WESTERN GREAT LAKES EARLY FRI MORNING. FRIDAY THROUGH EARLY NEXT WEEK... ENSEMBLES CONTINUE TO PROG A ROBUST TROUGH SLIDING SOUTH FROM CENTRAL CANADA FRI. THIS COUPLED WITH DOWNSTREAM MID-LVL RIDGING ACROSS THE SOUTHEAST CONUS WILL STRENGTHEN THE FRONTAL BOUNDARY THAT WILL BE ORIENTED FROM THE SOUTHERN PLAINS STRETCHING NORTHEAST THROUGH THE GREAT LAKES REGION INTO WESTERN QUEBEC. THIS SETUP IS IDEAL FOR THE DEVELOPMENT OF AN ATMOSPHERIC RIVER WITH ABUNDANT LOW LEVEL MOISTURE AND EFFICIENT PRECIP PRODUCING CONVECTION. OPER GUIDANCE HAS BEEN RELATIVELY CONSISTENT WITH BRINGING A SERIES OF WAVES ALONG THE SLOW MOVING FRONTAL BOUNDARY FRI AFTN/EVE...THEN THE BOUNDARY SHOULD SLIDE EAST WITH WINDS QUICKLY VEERING NORTH/NORTHEAST FOR SAT AND USHERING IN MUCH COOLER AIR TO THE REGION. CURRENT INDICATIONS ARE THAT HIGHS SAT MAY STRUGGLE TO WARM BEYOND THE UPR 50S ACROSS NORTHEAST IL/NORTHWEST IN...WITH ONLY LOW 60S ELSEWHERE. STRONG SFC RIDGE WILL REMAIN NORTH OF THE REGION...SO THE PRIOR FRONTAL BOUNDARY MAY BECOME QUASI-STATIONARY FOR THE WEEKEND ALONG THE OHIO VALLEY AND CONTINUE TO FEED PRECIP CHANCES TO THE SOUTHERN CWFA. BEACHLER && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 09Z... * SOUTH-SOUTHWEST WINDS OF AROUND 40 KT AT 1000 FT OVERNIGHT...SETTING UP THE POTENTIAL FOR LOW LEVEL WIND SHEAR. * MVFR CEILINGS PROBABLE AT TIMES TUESDAY WITH A CHANCE FOR TEMPORARY IFR. * PERIODS OF SHRA WITH PERIODIC TSRA FROM LATE TUESDAY MORNING THROUGH THE AFTERNOON. * NEAR DUE SOUTH WINDS ON TUESDAY WITH PERIODIC GUSTS POSSIBLE AND SOME VARIABILITY BETWEEN SOUTHEAST AND SOUTHWEST. KREIN //DISCUSSION...UPDATED 06Z... GUSTY SOUTH-SOUTHWEST WINDS HAVE DIMINISHED TO 10 KT OR LESS AND BECOME SOUTHERLY. A LOW-LEVEL JET WILL DEVELOP OVERHEAD WITH SSWLY-SWLY WINDS OF 40 KT TO 45 KT FLOW AT 1500-2000 FT UNTIL ARND 12Z. SOME THUNDERSTORMS MAY DEVELOP THROUGH OVERNIGHT AHEAD OF A FRONT FROM NRN MO THROUGH ERN IA AND INTO WI. THESE STORMS WILL ONLY MAKE SLOW PROGRESS EASTWARD DUE TO THE STRONG SSWLY-SWLY WINDS ALOFT SO...AND STORMS THAT DO DEVELOP SHOULD REMAIN NORTH AND NORTHWEST OF AREA TAF SITES...THOUGH THERE IS A CHANCE THAT A FEW STORMS COULD APPROACH THE RFD TERMINAL AREA VERY LATE TONIGHT. AS AN MID LEVEL DISTURBANCE MOVING FROM THE SOUTHERN PLAINS TO NRN IL BY TUESDAY AFTERNOON MAY BRING ANOTHER ROUND OF SHOWERS WITH SCT EMBEDDED THUNDERSTORMS TO THE REGION. UPPER LEVEL FORCING FROM THE MID LEVEL DISTURBANCE AND AN UPPER LEVEL JET STREAM WILL ENHANCE THE LIKELIHOOD FOR SHRA AND THE CHANCE FOR TSRA...WITH THE MOST LIKELY CHANCE FOR ACTIVITY FROM 15Z THROUGH 02Z. SOME UNCERTAINTY REMAINS IN PINNING DOWN THE EXACT PERIOD FOR THE TSRA...SO WILL MAINTAIN THE GOING TEMPO FOR LATE MORNING THROUGH EARLY AFTERNOON. HOWEVER...THE PCPN ACTIVITY COULD BE SHIFTED OR EXPANDED IN TIME. WINDS WILL BE SOUTHERLY ON TUESDAY...THOUGH DIRECTION MAY BE A BIT VARIABLE AROUND CONVECTIVE ACTIVITY...THOUGH A GENERALLY SOUTHERLY DIRECTION SHOULD PREVAIL THROUGH THE NIGHT AND MUCH OF THE DAY TUESDAY. SOME GUSTINESS IS POSSIBLE THROUGH THE ENTIRE DAY...WITH THE LATEST GUIDANCE SUGGESTING THAT WINDS COULD STRENGTHEN AND BECOME EVEN MORE GUSTY THROUGH THE NIGHT TOMORROW NIGHT WITH WINDS VEERING SWLY AS SURFACE LOW PRESSURE MOVES NORTHEAST ACROSS SOUTHERN WISCONSIN. KREIN //ORD AND MDW CONFIDENCE...UPDATED 09Z... * HIGH CONFIDENCE IN 40-45 KT SSWLY-SWLY FLOW ALOFT OVERNIGHT...BUT MEDIUM IN TRUE LLWS OCCURRING. * HIGH CONFIDENCE IN WIND TRENDS OVERNIGHT AND TUESDAY MORNING. MEDIUM IN WIND TRENDS TOMORROW EVENING. * MEDIUM CONFIDENCE IN MVFR CIGS TUESDAY MORNING WITH LOWER CONFIDENCE IN DURATION AND HOW LOW CIGS WILL DROP. * HIGH CONFIDENCE IN SHOWERS AND AT LEAST A PERIOD OF TSRA. LOW CONFIDENCE IN SPECIFIC TSRA TIMING AND IMPACT ON THE TERMINALS WITH MULTIPLE ROUNDS POSSIBLE BETWEEN 15Z AND 02Z. KREIN //OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z... WEDNESDAY...CHANCE OF TSRA. WEST WINDS. THURSDAY...SLIGHT CHANCE OF TSRA LATE AT NIGHT. SOUTHEAST WINDS. FRIDAY...INCREASING CHANCE OF TSRA THROUGH THE DAY AND NIGHT. SOUTHWEST WINDS. SATURDAY...SHRA LIKELY WITH A CHANCE OF TSRA. NORTHEAST WINDS. SUNDAY...CHANCE OF SHRA. EAST WINDS. MTF && .MARINE... 229 AM CDT WARM MOIST AIR CONTINUES TO FEED NORTH ACROSS THE LAKE TODAY...WHICH MAY HELP TO FURTHER ENHANCE ANY AREAS OF FOG THAT HAVE ALREADY DEVELOPED. IT IS POSSIBLE PATCHY DENSE FOG MAY DEVELOP...ALTHOUGH WINDS MAY BE JUST STRONG ENOUGH TO LIMIT THE COVERAGE AND INTENSITY OF THE FOG. A SURFACE LOW PRESSURE SYSTEM WILL BE LIFTING NORTH ACROSS EASTERN IOWA INTO CENTRAL WISCONSIN THIS EVENING. THE GRADIENT WILL TIGHTEN ACROSS THE CENTRAL/SOUTHERN PORTIONS OF THE LAKE...WHICH WITH WARMER NEARSHORE WATERS EXPECT SOME SLIGHTLY BETTER MIXING TO OCCUR. FURTHER OUT ACROSS THE OPEN WATERS THE WATER REMAINS COLD AND EXPECT THE STABILITY TO MAKE IT DIFFICULT TO MIX TO THE SFC THE HIGHER GUSTS. HIGH PRESSURE THEN ARRIVES LATE WEDNESDAY WITH LIGHT WINDS DEVELOPING. THEN HIGH PRESSURE SHIFTS EAST THURSDAY NIGHT...WITH SOUTHERLY WINDS DEVELOPING AGAIN FRIDAY. A FRONTAL BOUNDARY WILL APPROACH LAKE MICHIGAN LATE FRIDAY NIGHT THEN STEADILY SLIDE SOUTH ALONG THE LAKE. THIS WILL ALLOW WINDS TO QUICKLY VEER FROM SOUTH TO NORTH/NORTHEAST SATURDAY. ALONG WITH THIS QUICK WIND SHIFT WILL BE COOLER AIR SLIDING SOUTH OVER THE LAKE. WAVES SHOULD EASILY BUILD SATURDAY FOR THE CENTRAL/SOUTHERN PORTIONS OF THE LAKE. 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/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO

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