DAY 1 CONVECTIVE OUTLOOK CORR 1 NWS STORM PREDICTION CENTER NORMAN OK 0117 AM CDT MON MAY 20 2013 VALID 201200Z - 211200Z ...THERE IS A MDT RISK OF SVR TSTMS ACROSS PORTIONS OF OK/FAR SOUTHEAST KS/SOUTHERN MO/NORTHWEST AR/FAR NORTH TX... ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SOUTHERN PLAINS TO THE MIDWEST/GREAT LAKES REGION... CORRECTED FOR AREAS IN MODERATE RISK HEADLINE ...SYNOPSIS... YET ANOTHER ACTIVE/RELATIVELY WIDESPREAD SEVERE WEATHER DAY IS LIKELY ACROSS PORTIONS OF THE SOUTHERN PLAINS TO MIDWEST TODAY AND TONIGHT. A PROMINENT CENTRAL CONUS UPPER TROUGH WILL CONTINUE A GENERAL EASTWARD ADVANCEMENT THROUGH TONIGHT...WITH A LEAD/CLOSED UPPER LOW PIVOTING OVER THE DAKOTAS/UPPER MIDWEST. A SOUTHERN STREAM SHORTWAVE TROUGH/MODERATELY STRONG POLAR JET WILL EJECT EAST-NORTHEASTWARD OVER THE SOUTHERN ROCKIES TO THE SOUTHERN PLAINS/OZARKS...WITH SEVERE TSTMS INCREASINGLY LIKELY BY PEAK HEATING AND CONTINUING INTO TONIGHT. MEANWHILE...A LINGERING UPPER LOW OVER THE COASTAL SOUTHEAST STATES WILL CONTRIBUTE TO ANOTHER DAY OF WIDELY SCATTERED TO SCATTERED TSTMS OVER THE REGION...SOME OF WHICH MAY AGAIN BE STRONG OR SEVERE. ...SOUTHERN PLAINS/OZARKS/MIDDLE MS VALLEY... UNDER THE INFLUENCE OF BROAD/MODERATELY STRONG CYCLONIC FLOW ALOFT...THE AIRMASS IS EXPECTED TO AGAIN BECOME QUITE UNSTABLE ACROSS MUCH OF THE REGION BY THE AFTERNOON BENEATH AN ELEVATED MIXED LAYER EXTENDING ACROSS THE SOUTHERN PLAINS INTO PARTS OF THE OZARKS AND LOWER/MIDDLE MS VALLEY. MIDDLE/UPPER 60S AND SOME LOWER 70S F SURFACE DEWPOINTS WILL BE QUITE COMMON WITHIN A SPATIALLY BROAD WARM SECTOR AHEAD OF A COLD FRONT EXTENDING FROM AN EASTERN DAKOTAS/MN SURFACE LOW SOUTHWESTWARD TO NEAR THE KANSAS CITY AREA/EASTERN KS AND WESTERN OK...AND AHEAD OF A DRYLINE EXTENDING FROM SOUTHWEST OK SOUTHWARD INTO WESTERN NORTH TX/WEST-CENTRAL TX. OUTFLOW REMNANTS FROM OVERNIGHT/EARLY DAY CONVECTION ACROSS THE OZARKS/MIDDLE MS VALLEY WILL LIKELY BE A FACTOR INTO THIS AFTERNOON...POSSIBLY AS A RENEWED FOCUS FOR SEVERE TSTM REDEVELOPMENT...WITH THE MOST AGGRESSIVE HEATING/DESTABILIZATION ON THE WESTERN FRINGES OF THIS ACTIVITY ACROSS THE SOUTHERN PLAINS AND PERHAPS LOWER MO VALLEY JUST AHEAD OF THE TRUE SYNOPTIC COLD FRONT. SEVERE TSTMS CAPABLE OF HAIL/DAMAGING WINDS AND SOME TORNADO THREAT WILL BE POSSIBLE ALONG THIS FRONTAL ZONE ACROSS EASTERN KS/NORTHERN MO INTO THE UPPER MS VALLEY...WITH A PERSISTENT/EAST-NORTHEASTWARD DEVELOPING SEVERE THREAT INTO THE EVENING. THAT SAID...THE MOST INTENSE/MOST PROBABLE SEVERE STORMS ARE ANTICIPATED A BIT FARTHER SOUTH-SOUTHWEST ACROSS THE SOUTHERN PLAINS/OZARKS BY MID/LATE AFTERNOON INTO TONIGHT. THIS INCLUDES A PORTION OF THE SYNOPTIC FRONT AND/OR OUTFLOW ACROSS FAR SOUTHEAST KS/SOUTHWEST MO...AREAS ROUGHLY PARALLEL AND NORTHWEST OF THE I-44 CORRIDOR...BUT ESPECIALLY SOUTH-SOUTHWESTWARD INTO MUCH OF THE MIDDLE PART OF OK /POTENTIALLY INCLUDING OKC METRO/...TO NEAR THE HEAT-AIDED SURFACE LOW AND SOUTHWARD-EXTENDING SHARPENING DRYLINE INTO THE WESTERN PART OF NORTH TX/WEST-CENTRAL TX. IN THIS CORRIDOR...MLCAPE VALUES ARE LIKELY TO EXCEED 2500-3000 J/KG BY AFTERNOON WITHIN THE WARM SECTOR ACROSS OK AND WEST-CENTRAL/NORTH-CENTRAL TX...AND PERHAPS INTO PARTS OF SOUTHEAST KS AND MO. WITH BROAD/MODERATELY STRONG CYCLONIC MID-HIGH LEVEL FLOW /50+ KT AT 500 MB/ OVER THE REGION...40-50 KT OF EFFECTIVE SHEAR WILL COINCIDE WITH THE MAJORITY OF THE EFFECTIVE FRONTAL ZONE AND/OR DRYLINE ACROSS OK/EXTREME NORTH TX INTO SOUTHEAST KS AND THE OZARKS. THE DEGREE OF SHEAR AND MOISTURE/INSTABILITY WITHIN THE WARM SECTOR WILL FAVOR SCATTERED TO NUMEROUS SUPERCELL STRUCTURES...AT LEAST THROUGH MID-EVENING OF THE CONVECTIVE CYCLE. VERY LARGE HAIL AND TORNADOES ARE POSSIBLE WITH SUPERCELLS...WITH AN EARLY EVENING PEAK TORNADO THREAT /PERHAPS A COUPLE OF STRONG TORNADOES/ BOOSTED BY A NOCTURNALLY STRENGTHENING SOUTHERLY LOW LEVEL JET AND ASSOCIATED LOW-LEVEL HODOGRAPH ENLARGEMENT. ULTIMATELY...ONE OR MORE MCS/S SHOULD EVOLVE ALONG NOSE OF STRENGTHENING LOW LEVEL JET OVER OK AND EVENTUALLY INTO THE OZARKS BY LATE EVENING/OVERNIGHT. DAMAGING WIND POTENTIAL WILL LIKELY INCREASE IN ASSOCIATION WITH MCS DEVELOPMENT THIS EVENING....ASIDE FROM A SEVERE HAIL AND CONTINUED TORNADO RISK...BUT ON AN INCREASINGLY ISOLATED BASIS INTO LATE EVENING/OVERNIGHT. ...UPPER MIDWEST/GREAT LAKES... MID-LEVEL SHORTWAVE TROUGH/SPEED MAX WILL PIVOT NORTHEASTWARD OVER THE UPPER MIDWEST/UPPER MS VALLEY DURING THE AFTERNOON...WITH ASSOCIATED FORCING FOR ASCENT OVERSPREADING A RELATIVELY MOIST/UNSTABLE BOUNDARY LAYER TO THE SOUTH OF A WARM FRONT EXTENDING FROM THE EASTERN DAKOTAS/MN SURFACE LOW EASTWARD TO NORTHERN PORTIONS OF THE GREAT LAKES REGION. TWO GENERAL SCENARIOS FOR SEVERE TSTM DEVELOPMENT SEEM PROBABLE THIS AFTERNOON. ONE BEING PARTS OF IA/UPPER MS VALLEY ON THE EASTERN PERIPHERY OF THE UPPER LOW AND UPPER JET EXIT REGION AS IT COINCIDES WITH THE SYNOPTIC FRONT. MEANWHILE...FARTHER EAST...PROPAGATION OF REMNANT OUTFLOW /EVEN SUBTLE REMNANTS INTO AFTERNOON/ ARE A PLAUSIBLE INFLUENCE FOR RENEWED TSTM DEVELOPMENT INTO A VERY UNSTABLE AIRMASS ACROSS THE GREAT LAKES REGION. OVERALL...THIS INCLUDES POTENTIAL FOR SOME SUPERCELLS ASIDE FROM SUSTAINED LINEAR STRUCTURES...WITH BOUTS OF DAMAGING WINDS/SEVERE HAIL AND A COUPLE OF TORNADOES ALL POSSIBLE ACROSS THE REGION. ...SOUTHEAST STATES/FL... THE AIRMASS SHOULD STRONGLY DESTABILIZE THIS AFTERNOON...ESPECIALLY IN AREAS NEAR AND WEST-SOUTHWEST OF THE APPALACHIANS SPINE...WITH DIURNALLY INCREASING/INTENSIFYING TSTM DEVELOPMENT FURTHER AIDED BY A PERSISTENT UPPER LOW OVER THE REGION. BOUTS OF DAMAGING WINDS AND SOME HAIL WILL BE POSSIBLE AS STORMS GENERALLY DRIFT SOUTHWARD THROUGH THE AFTERNOON/EARLY EVENING HOURS. ..GUYER/MEAD.. 05/20/2013