VALID FOR TODAY (OCTOBER 13, 2014) SPC AC 131236 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0736 AM CDT MON OCT 13 2014 VALID 131300Z - 141200Z ...THERE IS A MDT RISK OF SVR TSTMS OVER PORTIONS ERN AR...NRN LA...NRN/WRN MS...WRN TN...SERN MO...EXTREME SRN IL...AND WRN KY... ...THERE IS A SLGT RISK OF SVR TSTMS ELSEWHERE FROM CENTRAL PORTIONS IL/INDIANA TO WRN/CENTRAL GULF COAST...TN VALLEY REGION AND WRN FL PANHANDLE... ...SUMMARY... STRONG TO SEVERE THUNDERSTORMS ARE EXPECTED TODAY AND TONIGHT FROM EAST TEXAS THROUGH THE LOWER AND MIDDLE MISSISSIPPI VALLEY TO PARTS OF THE TENNESSEE VALLEY...OHIO VALLEY AND GULF COAST STATES. WIDESPREAD DAMAGING WINDS AND A FEW TORNADOES ARE LIKELY...ESPECIALLY OVER THE MID SOUTH AND LOWER MISSISSIPPI VALLEY REGIONS TODAY. --- TECHNICAL DISCUSSION --- ...SYNOPSIS... HIGHLY AMPLIFIED PATTERN IS FCST THROUGH PERIOD...WITH PROGRESSIVE/SYNOPTIC-SCALE TROUGHS OVER NERN PAC AND MOVING EWD FROM CENTRAL CONUS. PRINCIPAL SHORTWAVE TROUGH IS EVIDENT IN MOISTURE-CHANNEL IMAGERY OVER WRN OK AND W-CENTRAL TX. AS THIS FEATURE MOVES ENEWD TODAY...500-MB CLOSED LOW SHOULD DEVELOP...REACHING OK/MO BORDER REGION BY 00Z WITH SHORTWAVE TROUGH SSWWD ACROSS MIDDLE TX COASTAL PLAIN. BY 12Z...STRENGTHENING MID/UPPER LOW SHOULD REACH E-CENTRAL MO...WITH AMPLIFIED TROUGHING EXTENDING NWD ACROSS UPPER MS VALLEY AND SWD OVER WRN LA. AT SFC...COMBINED SYNOPTIC/WAKE LOW WAS ANALYZED OVER NERN OK...FCST TO MOVE NEWD TO WRN IL BY END OF PERIOD WHILE 500-MB CYCLONE CATCHES UP TO MAKE ENTIRE CYCLONIC SYSTEM MORE VERTICALLY STACKED. STG COLD FRONT WILL SWEEP SEWD ACROSS OK...SWRN MO AND MOST OF CENTRAL/E TX BY 00Z...REACHING WRN MS...WRN TN AND WRN IL BY 12Z. HOWEVER...FRONT ITSELF SHOULD BE MINOR FACTOR IN MOST OF CONVECTIVE SCENARIO...PERHAPS OVERTAKING SRN PARTS OF QLCS SOONEST. ...MID-SOUTH TO GULF COAST AND OH VALLEY... REF WWS 532-534 AND ACCOMPANYING MESOSCALE DISCUSSIONS FOR NEAR-TERM THREAT AREAS. DAMAGING WINDS WILL BE PRIMARY THREAT FROM SVR TSTMS SWEEPING EWD OVER THIS CORRIDOR TODAY...THOUGH SPORADIC...MARGINALLY SVR HAIL ALSO MAY OCCUR. A FEW TORNADOES ALSO ARE POSSIBLE...WHETHER FROM MAIN QLCS OR FROM FOREGOING SUPERCELLS IN VERY MOIST...WEAKLY CAPPED WARM SECTOR TODAY AND TONIGHT. WELL-ORGANIZED QLCS...WITH HISTORY OF EFFECTIVELY JUMPING EWD TO POSITION OF YOUNGER/INTENSIFYING WARM-SECTOR TSTM BANDS...CONTINUES TO EXHIBIT THAT BEHAVIOR ATTM OVER E TX. RESULTING BAND OF STG-SVR TSTMS IS FCST TO PROCEED EWD ACROSS OUTLOOK AREA WITH INCREASING SVR RISK THROUGH AFTN...WHILE NRN END STRENGTHENS INVOF OZARKS AND ACCELERATES NEWD TOWARD LOWER OH VALLEY. TRANSLATION OF THIS CONVECTION ALREADY IS FASTER THAN ALL KINDS OF MODELS HAVE INDICATED...EVEN SHORT-FUSED/RADAR-ASSIMILATING GUIDANCE LIKE HRRR THAT SHOULD PERFORM BEST AT KEEPING UP WITH SUCH TENDENCIES. THIS SITUATION MAY PERSIST THROUGH MOST OF TODAY DESPITE SOME GUIDANCE SHOWING DECELERATION OF QLCS E OF MS RIVER. AS SUCH...OUTLOOK LINES HAVE BEEN SHIFTED/TRIMMED EWD IN DEFERENCE TO RECENT AND PROJECTED TRENDS. FOREGOING AIR MASS...THOUGH MOSTLY CLOUDY FROM AR AND MS NWD...SHOULD DESTABILIZE FROM COMBINATION OF WARM/MOIST ADVECTION AND POCKETS OF SFC DIABATIC HEATING. RESULTING BOUNDARY-LAYER THETAE INCREASE WILL OFFSET MODEST MIDLEVEL LAPSE RATES ENOUGH TO BOOST PRECONVECTIVE/AFTN MLCAPE TO 1500-2000 J/KG OVER PORTIONS MID-SOUTH AND LOWER MS VALLEY...DIMINISHING NWD THROUGH IL. MEANWHILE VERTICAL SHEAR WILL INCREASE WITH TIME PRIOR TO QLCS ARRIVAL...EXCEPT PERHAPS OVER PARTS OF S-CENTRAL/SE TX WHERE MORE MODEST INCREASE IN FLOW ALOFT MAY BE OFFSET IN SHEAR CALCULATIONS BY VEERING SFC WINDS. AS MID-UPPER TROUGH AMPLIFIES...FOREGOING WINDS ALOFT WILL BACK TO BECOME MORE MERIDIONAL...REDUCING BOTH 1. DEEP-LAYER DIRECTIONAL SHEAR AND 2. ALREADY SMALL COMPONENT OF WINDS ALOFT THAT ARE ORTHOGONAL TO BAND OF CONVECTIVE FORCING. IN FACT...FCST SOUNDINGS NEAR AND E OF MS RIVER...JUST AHEAD OF MAIN CONVECTIVE BAND...SHOW SOME BACKING OF WIND WITH HEIGHT IN VARIOUS PARTS OF 700-500-MB LAYER. THESE FACTORS FORETELL LIKELY MAINTENANCE OF DOMINANT QUASILINEAR MODE. EMBEDDED LEWP/BOW FEATURES STILL MAY DEVELOP CIRCULATIONS CAPABLE OF LOCALLY ENHANCED WIND-DAMAGE SWATHS AND SMALL/BRIEF TORNADOES. MEANWHILE...A FEW SUPERCELLS MAY DEVELOP AHEAD OF PRIMARY QLCS...ESPECIALLY FROM MID-SOUTH REGION THIS AFTN TO PORTIONS MS/AL THIS EVENING AND OVERNIGHT...IN REGIME OF RICH MOISTURE...LOW LCLS AND FAVORABLE HODOGRAPHS. AS SUCH...CATEGORICAL-THRESHOLD TORNADO PROBABILITIES HAVE BEEN EXPANDED SEWD ACROSS MS/AL...WHILE BEING TRIMMED ON WRN EDGE AS NOTED ABOVE DUE TO CONVECTIVE TRENDS. SVR-THREAT AREA MAY EFFECTIVELY PINCH OFF FROM NW-SE DURING MIDDLE-LATTER PARTS OF PERIOD AS MAIN CONVECTIVE REGIME OUTRUNS MOST FAVORABLE DESTABILIZATION. HOWEVER...SVR THREAT SHOULD PERSIST THROUGH TONIGHT ACROSS DIXIE PORTION OF OUTLOOK. ..EDWARDS/MOSIER.. 10/13/2014
Posted on: Mon, 13 Oct 2014 13:01:58 +0000
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