Chicago STP but NWS says capped. Severe event may be more WI and MN.
Posted by JAC on 4/10/2011, 6:43 am
 HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 501 AM CDT SUN APR 10 2011 ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019- 111015- WINNEBAGO-BOONE-MCHENRY-LAKE ILLINOIS-OGLE-LEE-DE KALB-KANE- DUPAGE-COOK-LA SALLE-KENDALL-GRUNDY-WILL-KANKAKEE-LIVINGSTON- IROQUOIS-FORD-LAKE INDIANA-PORTER-NEWTON-JASPER-BENTON- 501 AM CDT SUN APR 10 2011 /601 AM EDT SUN APR 10 2011/ THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL ILLINOIS... NORTHEAST ILLINOIS AND NORTHWEST INDIANA. .DAY ONE...TODAY AND TONIGHT. WEATHER HAZARDS EXPECTED: SOUTHERLY WINDS GUSTING TO AROUND 40 MPH. HEIGHTENED FIRE DANGER. AND THUNDERSTORMS...THE STRONGEST MAY PRODUCE: DAMAGING WINDS IN EXCESS OF 60 MPH. HAIL TO THE SIZE OF HALF DOLLARS. HEAVY DOWNPOURS. CLOUD TO GROUND LIGHTNING. AND POSSIBLY A TORNADO. AREAS AFFECTED AND TIMING: STRONG SOUTHERLY WINDS ARE LIKELY THIS AFTERNOON AND EVENING ACROSS THE ENTIRE OUTLOOK AREA. A HEIGHTENED GRASS FIRE DANGER IS EXPECTED THIS AFTERNOON. ALSO...ISOLATED THUNDERSTORMS COULD MOVE INTO WESTERN PORTIONS OF THE OUTLOOK AREA...GENERALLY WEST OF A ROCKFORD TO PERU LINE THIS EVENING. THUNDERSTORMS ARE THEN EXPECTED TO BECOME MORE WIDESPREAD AS THEY MOVE EAST ACROSS THE OUTLOOK AREA THIS EVENING...ESPECIALLY SOUTH OF INTERSTATE 80. DISCUSSION: A COLD FRONT WILL MOVE EAST INTO AN UNSEASONABLY WARM AIRMASS OVER THE REGION. INITIALLY...VERY WARM TEMPERATURES ALOFT ARE EXPECTED TO PREVENT THUNDERSTORM DEVELOPMENT...HOWEVER COOLING ALOFT THIS EVENING SHOULD ALLOW THUNDERSTORMS TO GRADUALLY BECOME MORE WIDESPREAD. MODERATE INSTABILITY AND STRONG WINDS ABOVE THE SURFACE WILL CREATE A FAVORABLE ENVIRONMENT FOR SEVERE THUNDERSTORMS. THE PRIMARY THREATS WILL BE LARGE HAIL AND DAMAGING WINDS...BUT CONDITIONS WILL ALSO BECOME SOMEWHAT FAVORABLE FOR TORNADOES THIS EVENING...HOWEVER IT NOW APPEARS MOST OF THE STORMS WILL FORM IN A LINE AS OPPOSED TO INDIVIDUAL SUPERCELLS. SHOULD THIS BE THE CASE...IT WOULD LIMIT THE POTENTIAL FOR A MORE WIDESPREAD OR SIGNIFICANT TORNADO THREAT. SOUTHERLY WINDS WILL GUST TO AROUND 40 MPH THIS AFTERNOON AND EVENING. THE STRONG WINDS COMBINED WITH RELATIVE HUMIDITY VALUES FALLING BELOW 40 WILL LIKELY LEAD TO A HEIGHTENED GRASS FIRE DANGER. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY. THERE IS A CHANCE OF THUNDERSTORMS THURSDAY INTO THURSDAY NIGHT. .SPOTTER INFORMATION STATEMENT... SPOTTERS MAY BE NEEDED THIS EVENING. && AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 413 AM CDT SUN APR 10 2011 .DISCUSSION... 359 AM CDT SHORT TERM (TODAY THROUGH TUESDAY NIGHT)... FORECAST CHALLENGES THIS MORNING ARE NUMEROUS...INCLUDING: * SEVERE POTENTIAL THIS EVENING * NEAR RECORD WARMTH TODAY * STRONG WINDS TODAY * FIRE WEATHER CONCERNS THIS AFTERNOON REALLY PULLING OUR HAIR OUT THIS MORNING AS MODEL GUIDANCE HAS MADE SOME SIZABLE ADJUSTMENTS FROM PREVIOUS RUNS. MOST NOTABLY...THE WEAK PRE-FRONTAL TROUGH/CONVERGENCE ZONE ADVERTISED IN THE 12Z GUIDANCE IS GONE THIS FAR NORTH. IN ADDITION...UPPER LOW IS PROGGED TO BE MUCH WEAKER/MORE POSITIVELY TILTED RESULTING IN LESSER HEIGHT FALLS AND LARGE SCALE ASCENT OVER THE WARM SECTOR THIS AFTERNOON/EVENING. GIVEN THE PRESENCE OF VERY IMPRESSIVE EML AS SAMPLED BY UPSTREAM 00Z RAOBS (SGF/TOP/OAX)...WEAKER LARGE SCALE ASCENT TO LIFT THROUGH CAP...AND ABSENCE OF PRE-FRONTAL TROUGH IN LATEST GUIDANCE...THE CONFIDENCE IN PRE-FRONTAL CONVECTION DEVELOPING HAS DECREASED SUBSTANTIALLY. IN FACT...HARD TO FIND A MODEL THATS STILL SHOWING ANY PRE-FRONTAL DEVELOPMENT AND MANY ARENT DEVELOPING ALL THAT MUCH CONVECTION EVEN ALONG THE FRONT OVER THE CWA. AS ALLUDED TO YESTERDAY...AFTERNOON ENVIRONMENT WILL BE PRETTY UNFAVORABLE FOR TORNADOES WITH VERY HIGH LCL HEIGHTS. REGARDING TORNADO POTENTIAL THIS EVENING...BIG QUESTIONS HAVE NOW ARISEN REGARDING EXTENT OF CONVECTIVE DEVELOPMENT. IN ADDITION...ANY STORMS THAT DO DEVELOP ARE LOOKING TO BE TIED MORE TO THE COLD FRONT...WHERE CLOUD BEARING LAYER SHEAR VECTORS ARE PROGGED TO BE ORIENTED PARALLEL TO THE INITIATING BOUNDARY...SO THE POTENTIAL FOR DISCRETE STORMS IS LOOKING DRAMATICALLY LOWER THAN PREVIOUSLY FEARED. WHILE CONDITIONS WILL BECOME MORE FAVORABLE FOR TORNADOES THIS EVENING WITH LOWERING LCL HEIGHTS AND VERY STRONG LOW LEVEL SHEAR AS LLJ INTENSIFIES...TORNADO THREAT WILL BE LARGELY CONDITIONAL ON STORM MODE...WHICH NOW APPEARS TO BE MORE LINEAR AND THUS A FAR LESSER (THOUGH NOT QUITE ZERO) TORNADO THREAT. GIVEN THE PRESENCE OF STRONG SHEAR AND STEEP LAPSE RATES/MODERATE INSTABILITY...ANY STORMS THAT DO DEVELOP WOULD CERTAINLY CARRY A RISK FOR LARGE HAIL AND DAMAGING WINDS...THOUGH THIS IS NO LONGER LOOKING LIKE A HIGHER END THREAT. MOST LIKELY CONVECTIVE SCENARIO NOW APPEARS TO BE SUPERCELLULAR STORM DEVELOPMENT WELL TO OUR NORTHWEST OVER MN/WI...CLOSER TO THE STRONGER/DEEPER ASCENT AND WEAKER CAP. ADDITIONALLY...CONVECTION WILL LIKELY DEVELOP OVER MISSOURI AS COLD FRONT OVER TAKES PRE- FRONTAL TROUGH/DRYLINE TOWARD EVENING...WITH THOSE STORMS PROGGED TO DEVELOP NORTHWARD AS THEY MOVE EAST. SEEMS QUITE LIKELY STORM MODE WITH THIS CONVECTION WILL BE LARGELY LINEAR...SO MAINLY A WIND AND MODEST HAIL THREAT WITH A MUCH MORE LIMITED TORNADO POTENTIAL. VERY STRONG CAP AT BASE OF THE EML SHOULD RESULT IN LITTLE IF ANY CUMULUS THIS AFTERNOON WITH ANY CIRRUS LIKELY OUT OF THE REGION BY MID MORNING. THIS WILL LEAVE SKIES SUNNY WITH STRONG/STRENGTHENING SOUTHERLY WINDS LIKELY ALLOWING TEMPS TO SOAR WELL INTO THE 80S TO NEAR 90F. ASSUMING WE CLIMB INTO THE UPPER 80S/NEAR 90F AS EXPECTED THAT WILL ALSO RESULT IN DEWPOINTS MIXING OUT...MEANING EVEN WEAKER INSTABILITY AND RAISING FIRE WEATHER CONCERNS (SEE FIRE WEATHER SECTION BELOW). DEEP MIXING INTO STEADILY INCREASING LOW LEVEL FLOW SHOULD RESULT IN WINDS INCREASING TO 20-30MPH WITH GUSTS TO AROUND 40MPH BY LATER THIS AFTERNOON. WINDS SHOULD BE SLOW TO DECREASE THIS EVENING AS DEEP AND SLOWLY INTENSIFYING SFC LOW PREVENTS FULL DECOUPLING...IN FACT WITH VERY STRONG LOW LEVEL JET WE COULD SEE SOME OF THE STRONGEST GUSTS THIS EVENING. FOR NOW HAVE KEPT WINDS JUST BELOW ADVISORY CRITERIA IN THE GRIDS BUT WE COULD GET CLOSE AND THIS WILL BE SOMETHING FOR THE DAY SHIFT TO WATCH. AFTER FRONT PASSES TONIGHT STRONG WEST WINDS WILL BEGIN TO USHER IN DRIER AND PROGRESSIVELY COOLER AIR MASS. AFTER A BRIEF SHOT OF CLEARING BEHIND THE FRONT LATE TONIGHT/EARLY MONDAY...LOOK FOR CLOUDS TO INCREASE AGAIN WITH A CHANCE OF SOME SHOWERS AS UPPER TROUGH AND ASSOCIATED COLD POOL MOVE ACROSS THE REGION MONDAY AFTERNOON. UPPER TROUGH THEN PUSHES EAST ALLOWING FOR CLEARING SKIES AND SEASONABLY COOL WEATHER TUESDAY. IZZI LONG TERM (WEDNESDAY THROUGH SATURDAY)... A MID/UPPER LOW WILL ESTABLISH ITSELF ACROSS THE NORTHEASTERN PACIFIC BY THE MIDDLE OF NEXT WEEK. THIS LOOKS TO PRODUCE A GOOD CHANCE OF RAIN SHOWERS ACROSS THE AREA AS ENERGY EMANATING FROM THIS LOW TRACKS ACROSS THE CENTRAL ROCKIES AND EVENTUALLY ACROSS THE PLAINS. AS THIS OCCURS...THE GUIDANCE SUGGESTS THAT A BUILDING DOWN STREAM RIDGE ACROSS THE WESTERN GREAT LAKES COULD LEAD TO THE UPPER TROUGH CLOSING OFF ACROSS THE MID MISSISSIPPI VALLEY. THIS WOULD LIKELY RESULT IN A SLOW SYSTEM MOVEMENT ACROSS THE CENTRAL UNITED STATES AND THUS RESULT IN A SEVERAL PERIODS OF RAIN SHOWERS. TEMPERATURES LOOK TO BECOME COOL BY THE END OF THE WEEK...ESPECIALLY IF THE COLD UPPER LOW MOVES ACROSS NORTHERN ILLINOIS AS SOME OF THE GUIDANCE SUGGESTS. ALTHOUGH THE MODEL AND ENSEMBLE GUIDANCE SHOWS SOME TIMING AND STRENGTH DISCREPANCIES WITH THIS SYSTEM...OVERALL...THERE IS BELOW AVERAGE SPREAD AMONG THE ENSEMBLES...ESPECIALLY THROUGH FRIDAY. THEREFORE CONFIDENCE IN THE EMERGING PATTERN IS DECENT GIVEN THAT THIS IS 5 TO 6 DAYS AWAY. KJB && .FIRE WEATHER... 413 AM CDT AS MENTIONED ABOVE...UNSEASONABLY WARM CONDITIONS ARE EXPECTED TODAY. DEWPOINTS CURRENTLY IN THE UPPER 50S/LOWER 60S ARE LIKELY TO FALL SOMEWHAT THIS AFTERNOON AS FULL SUNSHINE AND STRONG WINDS PROMOTE DEEP MIXING ALLOWING SOME OF THE LOWER DEWPOINTS ALOFT TO MIX TO THE SURFACE. DEWPOINTS SUNDAY AFTERNOON FELL INTO THE MID 50S UPSTREAM OVER ARKANSAS AND SOUTHERN MISSOURI WHERE TEMPS PEAKED NEAR 90 AND SEE NO REASON THEY WONT FOLLOW SUIT HERE THIS AFTERNOON. ASSUMING WE CAN MAINTAIN AT LEAST MID 50 DEWPOINTS...THEN RH VALUES WOULD REMAIN ABOVE RED FLAG CRITERIA (25%). HOWEVER...AS WINDS BEGIN TO GUST TO 40 MPH THIS AFTERNOON EXPECT A VERY HIGH FIRE DANGER FOR QUICKER DRYING FUELS SUCH AS GRASS. PLAN TO HIGHLIGHT THIS POTENTIAL IN FWF AND HWO. IZZI |
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In this thread:
Significant Severe Outbreak Today Upper MS Valley - JAC, 4/10/2011, 6:34 am
- Watch coming up - JAC, 4/10/2011, 2:57 pm
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