Expires:No;;383698 FXUS63 KLOT 191613 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 1113 AM CDT SUN MAY 19 2013 .MESOSCALE DISCUSSION... 1111 AM CDT THE MAIN CHALLENGES WILL BE THE CHANCES FOR CONVECTIVE ACTIVITY OVER THE NEXT FEW DAYS. FOR TODAY IT APPEARS THAT MOST IF NOT ALL OF THE AREA WILL REMAIN DRY. AIRCRAFT SOUNDINGS AND VARIOUS MODEL ANALYSIS INDICATE THAT AN EML CAPPING INVERSION HAS SET UP ACROSS MOST OF NORTHERN ILLINOIS WITH 700 MB TEMPERATURES NEAR 10C. WITH THE MID LEVEL ENERGY EXPECTED TO REMAIN WEST OF THE AREA DURING THE DAY TODAY...I DO NOT SEE ANYTHING THAT WILL ALLOW FOR CONVECTION TO BREAK OUT ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA DURING THE DAY TODAY. WITH THAT BEING SAID...A COUPLE OF STRONG THUNDERSTORMS HAVE DEVELOPED ACROSS FAR NORTHEASTERN MISSOURI AND FAR WEST CENTRAL ILLINOIS OVER THE PAST HOUR. THESE STORMS ARE DEVELOPING ALONG THE WESTERN PERIPHERY OF THE EML...WHERE COOLER MID LEVEL TEMPERATURES ARE IN PLACE. I EXPECT THESE STORMS TO MOVE TO THE NORTH-NORTHEAST. STORMS WILL LIKELY CONTINUE TO DEVELOP WEST OF THE AREA ACROSS IOWA THROUGH THE AFTERNOON AS THE MID LEVEL FLOW REMAINS STRONGER AND MORE DISTURBED. ALTHOUGH IT IS NOT OUT OF THE QUESTION THAT SOME OF THIS ACTIVITY COULD AFFECT NORTHWESTERN ILLINOIS AND POSSIBLY SOME OF MY FAR WESTERN COUNTIES LATER THIS AFTERNOON...THE OVERALL THREATS FOR CONVECTION THROUGH THIS AFTERNOON SHOULD RAPIDLY DECREASE TO THE EAST. WE WILL KEEP THE FORECAST DRY AS A RESULT...BUT WILL KEEP AN EYE ON THE CONVECTIVE ACTIVITY TO THE SOUTHWEST TO SEE IF ANY POPS WILL BE NEEDED FAR WEST LATER TODAY. A MORE SUBSTANTIAL DISTURBANCE...ASSOCIATED WITH THE UPPER JET ACROSS THE SOUTHWEST CONUS THROUGH THE TEXAS PANHANDLE...IS FORECAST TO PUNCH EAST-NORTHEASTWARD ACROSS MISSOURI TONIGHT. THIS LOOKS TO INDUCE VEERING LOW LEVEL JET AND MID LEVEL HEIGHT FALLS ACROSS THE AREA INTO MONDAY MORNING. THIS COULD RESULT IN A COMPLEX OF CONVECTION MOVING ACROSS THE AREA LATER TONIGHT INTO MONDAY MORNING WITH A WEAKENING CAP...AND THIS ACTIVITY COULD RESULT IN A SEVERE THUNDERSTORM RISK FOR PORTIONS OF THE AREA INTO MONDAY. KJB && .DISCUSSION... 501 AM CDT FORECAST FOR TODAY INTO LATE IN THE WEEK PRIMARILY HINGES ON HOW LONG IT TAKES FOR THE UPPER LOW THAT HAS BEEN FORMING OVER UT YESTERDAY AND OVERNIGHT TO REACH AND THEN FINALLY MOVE EAST OF THE LOCAL AREA. MODEL RUNS OVER THE LAST COUPLE OF DAYS HAVE ALL BEEN GRADUALLY SLOWING ITS EASTWARD PROGRESS AND ARE QUITE SIMILAR IN LOCATION OF THE UPPER LOW AS IT MOVES VERY SLOWLY ENE ACROSS THE PLAINS. MODELS ARE ALSO VERY SIMILAR IN THE GRADUAL WEAKENING OF THE UPPER LOW DURING TUE NIGHT AND WED AS IT MOVES TO THE UPPER MIDWEST...AND WITH THE REMAINING UPPER TROUGH STILL HANGING BACK ACROSS THE GREAT LAKES...OH VALLEY AND MS VALLEY DURING THU. WITH THE VERY SLOW PROGRESSION OF THIS SYSTEM ACROSS THE CENTRAL U.S. THE POTENTIAL FOR SHOWERS AND THUNDERSTORMS WILL HANG OVER THE LOCAL AREA FROM LATE TODAY TIL AT LEAST THU BEFORE THE UPPER TROUGH MOVES FURTHER OVER THE GREAT LAKES AND MIDWEST. ECMWF 00Z RUN IS MOST AGGRESSIVE WITH EASTWARD PROGRESS DURING THE LATTER PART OF THE WEEK...AS WAS THE PREVIOUS 12Z RUN. OTHER MODELS ARE SLOWER WITH ABSORBING THE GREAT LAKES UPPER TROUGH INTO THE DEEP VORTEX PROGGED TO SETTLE SOUTHWARD OVER EASTERN CANADA AND NORTHERN NEW ENGLAND WED THROUGH FRI BUT ALL HAVE THE UPPER TROUGH AXIS MOVING E OF THE LOCAL AREA BY FRI WITH A SURFACE RIDGE SPREADING SSE ACROSS THE REGION THU NIGHT THROUGH SAT. AHEAD OF THE SLOW MOVING SYSTEM VERY WARM AND MOIST AIR WILL CONTINUE TO SPREAD FROM THE SOUTHERN AND CENTRAL PLAINS NNE ACROSS THE MID MS VALLEY TODAY AND TONIGHT. FORECAST LOCAL TEMPERATURE PROFILES SHOW A CAPPING INVERSION IN PLACE TODAY BUT ERODED AWAY THIS EVENING. SURFACE DEW POINTS HAVE HELD STEADY ACROSS THE AREA DURING THE OVERNIGHT AND WILL GRADUALLY RISE AS INCREASING SE TO SSE LOW LEVEL FLOW ADVECTS MID 60S DEW POINTS OVER THE AREA. WITH RISING LOW LEVEL MOISTURE...THE REMOVAL OF THE CAP AND SLIGHT COOLING IN THE MID LEVELS BY THIS EVENING CAPE VALUES CLIMB TO 1.0 TO 1.5K BY LATE AFTERNOON AND TO 1.5 TO 2.0K DURING THE EARLY EVENING. ALL MODELS SHOW INDICATIONS OF A SHORT WAVE TROUGH ROTATING ACROSS NORTHERN MO AND IA TONIGHT. THIS WILL PROVIDE LARGE SCALE UVV TO SUSTAIN CONVECTION EXPECTED TO BE ONGOING UPSTREAM THIS AFTERNOON AND SPREADING OVER THE MID MS VALLEY DURING THE AFTERNOON. WITH INSTABILITY AND UPPER FORCING CHANCES FOR THUNDERSTORMS WILL SPREAD OVER MUCH OF FA LATE THIS AFTERNOON AND THIS EVENING... ESPECIALLY THE NW HALF. CONVECTIVELY INDUCED VORT MAXIMA ARE LIKELY TO MOVE NE AND E UP AND OVER THE UPPER RIDGE...CURRENTLY OVER THE MS VALLEY...AS THE RIDGE SHIFTS GRADUALLY E TO THE WESTERN GREAT LAKES AND THE LOWER OH VALLEY BY 00Z. HOWEVER...WITH A CAP IN PLACE DURING THE DAYTIME FORESEE ONLY SLIGHT CHANCES OF STORMS REACHING THE WESTERN FA BEFORE LATER AFTERNOON. MODELS USUALLY HAVE TROUBLE WITH IDENTIFYING AND MAINTAINING MINOR DISTURBANCES ROTATING AROUND AN UPPER LOW...ESPECIALLY WHEN NUMEROUS STRONG THUNDERSTORM COMPLEXES FORM. GIVEN LARGE UNCERTAINTY IN WHEN ANY DISTURBANCES WILL BE MOVING OVER THE LOCAL AREA WILL HAVE TO USE A BROAD BRUSH WITH POP VALUES MON THROUGH THU AS IDENTIFYING TIMES OF ANY PEAKS AND LULLS IN CONVECTIVE OCCURRENCE MINIMAL AT BEST IN THIS PATTERN. CIRRUS FROM PLAINS THUNDERSTORMS HAS BEEN SPREAD E OVERNIGHT BUT DISSIPATING AS IT REACHES THE UPPER RIDGE AXIS JUST W OF THE FA AT PREDAWN. EXPECT A GRADUAL INCREASE IN HIGH CLOUDINESS AS THE DAY PROGRESSES WITH THE RIDGE AXIS MOVING E OF THE FA BY EARLY EVENING. WITH SUFFICIENT SUN BEFORE THICKER CLOUDS SPREAD E TEMPS LIKELY TO HIT MID 80S AND POSSIBLY UPPER 80S...EXCEPT FOR ALONG THE LAKE WHERE THE SE LOW LEVEL WINDS WILL KEEP LAKE COOLED AIR AT THE IL SHORE. WITH 850HPA TEMPS PROGGED TO REMAIN AROUND VALUES SEEN TODAY FOR MON...GIVEN SOME SUN TEMPS ARE LIKELY BE SIMILAR TO TODAY OR EVEN A DEGREE OR TWO WARMER AS TEMPS TO START OUT IN THE UPPER 60S AT SUNRISE MON. INCREASING CONVECTION AND SHIFT EASTWARD OF THERMAL AXIS BY TUE WILL RESULT IN TEMPS IN THE UPPER 70S AND LOWER 80S... AND CONTINUED COOLING OFF MID AND LATE WEEK. BY FRI WITH THE LARGE SURFACE RIDGE BUILDING SSE OVER THE AREA AND MUCH COOLER AIR SPREADING DOWN FROM CENTRAL CANADA HIGHS ARE EXPECTED TO BE IN THE MID AND UPPER 60S INLAND...WITH AREAS NEAR THE LAKE IN THE 50S AND LOWER 60S WITH A MODERATELY STRONG ALMOST FULL-FETCH FLOW DOWN THE LAKE AND ACROSS NW IND AND NE IL. TRS && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 16Z... * LIGHT EAST TO SOUTHEAST WIND INCREASING TO 10-13KT WITH OCCASIONAL GUSTS TO 20KT EARLY THIS AFTERNOON. BECOMING MORE SOUTHERLY EARLY THIS EVENING. * DRY WEATHER SHUD HOLD MUCH OF THE DAY...PSBL TSRA LATE THIS EVENING. MAY BRING PATCHY MVFR CIGS WITH PRECIP. * WINDS DIMINISH OVERNIGHT TO ARND 8-10KT...THEN BREEZY CONDS RETURN DURING THE DAY MON. GUSTS COULD APPROACH 20-25KT. PAW //DISCUSSION...UPDATED 12Z... ONGOING CONVECTION THIS MORNING ACROSS EASTERN PORTIONS OF SOUTHEAST MINNESOTA STRETCHING SOUTH THROUGH EASTERN IOWA. THIS AREA OF SHOWERS/THUNDERSTORMS WAS STEADILY DISSIPATING AND NOT EXPECTED TO REACH NORTHERN IL/NORTHWEST IN AIRFIELDS. WITH WINDS RELATIVELY LIGHT EARLY THIS MORNING AND ADDITIONAL MOISTURE LIFTING OVERHEAD...VSBYS HAVE BEEN REDUCED SLIGHTLY TO AROUND 5-6SM AT MANY AIRFIELDS. THIS SHUD QUICKLY IMPROVE TO GREATER THAN 6SM BY 14Z. WINDS WILL BE VRB AT 4-6KT...THEN WITH SFC HEATING...WINDS WILL QUICKLY TURN SE AND INCREASE IN SPEED TO ARND 10-12KT. BETTER MIXING WILL ALLOW OCCASIONAL GUSTS BY MIDDAY TO 20KT FROM A 160-180 DEG RANGE. A FEW CUMULUS CLOUDS WILL DEVELOP LATER THIS MORNING...WITH BASES GENERALLY ARND 4-5KFT AGL. COVERAGE SHUD REMAIN IN A SCT CATEGORY...WITH SLIGHTLY BETTER COVERAGE LATE THIS AFTN. ENOUGH RIDGING REMAINS IN PLACE TO KEEP PRECIP/THUNDERSTORMS WEST OF THE AREA THRU SUNSET. GUIDANCE HAS SLOWED THE ARRIVAL OF CONVECTION UNTIL AFT 06Z...AND THERE ARE SOME INDICATIONS THAT THIS COULD GET PUSHED BACK UNTIL CLOSER TO DAYBREAK MON. COVERAGE OF THUNDERSTORMS DOES NOT LOOK TO HIGH AT THIS POINT. BEACHLER //ORD AND MDW CONFIDENCE...UPDATED 16Z... * MEDIUM/HIGH CONFIDENCE IN WIND TREND. * MEDIUM/HIGH CONFIDENCE AIRFIELDS WILL REMAIN DRY THRU THIS EVENING. * MEDIUM CONFIDENCE THUNDERSTORMS WILL HOLD OFF UNTIL AFT 06Z MON. PAW //OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z... MONDAY NIGHT...PERIODS OF TSRA. TUESDAY...PERIODS OF TSRA. WEDNESDAY...LIKELY TSRA DURING THE DAY. CHC OF SHRA IN THE EVENING. THURSDAY...CHC OF SHRA/TSRA EARLY. FRIDAY THROUGH SATURDAY...VFR. BEACHLER && .MARINE... 257 AM CDT AN AREA OF HIGH PRESSURE CONTINUES TO DRIFT EAST...WITH MUCH LESS OF AN INFLUENCE OVER LAKE MICHIGAN TODAY. MEANWHILE A WEAK FRONTAL BOUNDARY WAS BEGINNING TO APPROACH THE SOUTHERN TIP OF THE LAKE. A DEVELOPING AREA OF LOW PRESSURE CENTERED OVER THE CENTRAL PLAINS WILL STRUGGLE TO LIFT NORTH TODAY...AS A SECOND AREA OF HIGH PRESSURE BECOMES CENTERED ACROSS CENTRAL CANADA. ANOTHER FRONTAL BOUNDARY WILL BEGIN TO DROP SOUTH ACROSS THE NORTHERN PORTION OF THE LAKE THIS AFTERNOON/EVENING. AS THE CENTRAL PLAINS LOW PRESSURE STRENGTHENS...THIS WILL AID IN LIFTING A WARM FRONT ACROSS THE LAKE DURING THE DAY MONDAY. AS A RESULT MUCH WARMER AIR WILL PUSH OVER THE COLDER LAKE SFC...CREATING A RATHER MODEST STABLE ENVIRONMENT. THIS WILL POSE A CHALLENCE TO FORECASTING WAVE HEIGHTS AS WINDS MAY BE BETWEEN 10 TO 20 KT ABOVE THE SFC...BUT RIGHT AT THE SFC OF THE LAKE IT MAY NOT BE ABLE TO BUILD WAVES. THIS MAY CONTINUE WAVES AT 2 FT OR LESS FOR A MUCH LONGER PERIOD OF TIME...HOWEVER HAVE ADJUSTED THE OPEN WATERS FORECAST TO REFLECT A SLIGHT INCREASE IN WAVES. AS CONFIDENCE IN THE STRENGTH OF THE STABLE ENVIRONMENT IS LOW AT THIS TIME. ANOTHER ITEM OF CONCERN IS THE EXPECTED DEVELOPMENT OF PATCHY DENSE FOG. IN ADDITION TO THE MUCH WARMER AIR LIFTING NORTH ACROSS THE LAKE...THIS AIRMASS WILL ALSO HAVE AN ABUNDANCE OF MOISTURE. DEW POINTS WILL BE BETWEEN 5 AND 10 DEG WARMER THAN THE LAKE SFC TEMPS...WHICH WILL MOST LIKELY RESULT IN PATCHY DENSE FOG. THIS COULD LINGER THRU THE FIRST HALF OF THE WEEK. THE LOW PRESSURE WILL BEGIN TO PUSH EAST TOWARDS THE MID MISSISSIPPI VALLEY...REACHING THE OHIO VALLEY LATE IN THE WEEK. THIS SHOULD ALLOW WARM FRONT TO SAG TO THE SOUTH DURING THE WEEK. DURING THIS TIME...THE WIND DIRECTIONS WILL PRIMARILY BECOME EAST NORTHEASTWARD 15 TO 25 KT NORTH OF THE FRONT. LATER IN THE WEEK...AS THE SURFACE LOW PASSES EAST OF LAKE MICHIGAN...THE WINDS LOOK TO BE RATHER STOUT UP TO 25 TO POSSIBLY AS HIGH AS 30 KT OUT OF THE NORTH FOR A PERIOD AS A GOOD AREA OF HIGH PRESSURE BUILDS EASTWARD ACROSS ONTARIO AND THE UPPER GREAT LAKES REGION. BEACHLER && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. 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