The SPC is forecasting ...severe thunderstorms expected from eastern and southern texas into the lower mississippi valley this afternoon and tonight.... Please read the latest public statement about this event.
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SPC AC 160543 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1143 PM CST FRI FEB 15 2008 VALID 161200Z - 171200Z ...THERE IS A MDT RISK OF SVR TSTMS PORTIONS S-CENTRAL TX...MID/UPPER TX COASTAL PLAIN...TO E-CENTRAL TX... ...THERE IS A SLGT RISK OF SVR TSTMS ELSEWHERE FROM PORTIONS W-CENTRAL/SW TX TO LOWER TX COAST...ARKLATEX REGION...MUCH OF LA...AND WRN MS.... OUTBREAK OF SVR TSTMS -- PERHAPS INCLUDING SUPERCELLS WITH SIGNIFICANT TORNADOES -- APPEARS MOST PROBABLE FROM S-CENTRAL TX ACROSS COASTAL PLAIN INTO E TX DURING AFTERNOON AND EVENING. DAMAGING CONVECTIVE WINDS SHOULD BE COMMON WITH THIS SYSTEM...AND NUMEROUS REPORTS OF LARGE HAIL ALSO MAY OCCUR. ...SYNOPSIS... MAIN UPPER AIR FEATURE FOR THIS FCST PERIOD WILL BE UPPER LOW -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER EXTREME SERN AZ. THIS CYCLONE IS FCST TO MOVE EWD ACROSS LOWER PECOS VALLEY BEFORE TURNING NEWD OVER ERN OK LATE IN PERIOD..IN RESPONSE TO APPROACH OF SHORTWAVE TROUGH NOW DIGGING SEWD ACROSS PACIFIC NW. AT SFC...COMPLEX PATTERN SHOWS THREE MAIN FEATURES ATTM... 1. ARCTIC FRONTAL ZONE -- ANALYZED INITIALLY FROM ARKLATEX REGION SWWD ACROSS CLL/SAT AREAS TO FRONTAL-WAVE CYCLONE BETWEEN COT-DRT...THEN SWWD INTO MOUNTAINS OF CENTRAL COAHUILA. THIS FRONT IS FCST TO PIVOT CYCLONICALLY EARLY IN PERIOD...MOVING SEWD ACROSS RIO GRANDE VALLEY WHILE RETREATING SLIGHTLY NWWD OVER CENTRAL/N TX. THIS WILL OCCUR AS LEESIDE LOW -- INITIALLY OVER NERN MEX...MOVES/REFORMS NEWD OVER N-CENTRAL TX. BY 17/00-03Z TIME FRAME...WELL-DEFINED SFC LOW SHOULD BE OVER SERN OK WITH FRONT MOVING EWD/SEWD OVER E-CENTRAL TX AND COASTAL BEND REGION. BY 17/12Z...EXPECT OCCLUDED/STACKED CYCLONE FROM SFC-500 MB OVER MO OZARKS...COLD FRONT SWD ACROSS LA AND NWRN GULF. 2. DRYLINE...DIFFICULT TO LOCATE PRECISELY ATTM BUT EVIDENT OVER PIEDMONT REGION BETWEEN MEX SERRANIAS DEL BURRO RANGE AND RIO GRANDE. THIS FEATURE MAY MOVE E OF RIO GRANDE THROUGH EARLY-MID AFTERNOON...OVER PORTIONS DEEP S TX...BEFORE BEING OVERTAKEN BY COLD FRONT. 3. MARINE WARM FRONT...ANALYZED INITIALLY FROM ABOUT 125 SSW MSY...JUST S OF GLS...TO FAYETTE COUNTY TX...INTERSECTING ARCTIC BOUNDARY ABOUT 40 NNE VCT. THIS DENOTES NRN EDGE OF HIGH THETAE GULF AIR WITH DEW POINTS UPPER 60S TO LOW 70S F. WARM FRONT SHOULD LIFT NWD ACROSS CENTRAL AND SE TX FASTER THAN OVER SWRN LA. THIS WILL CAUSE TRIANGULAR WEDGE OF RICHEST WARM SECTOR AIR TO LIFT NWD ACROSS E TX BEFORE COLD FROPA. WARM SECTOR EXPANSION FARTHER NE OVER LA AND ARKLATEX REGION PROBABLY WILL BE IMPEDED/PREVENTED BY CLOUDS AND PRECIP. ...S-CENTRAL TX TO SWRN LA...WARM SECTOR... GREATEST COVERAGE OF TSTMS IS FCST INVOF COLD FRONT WHERE LINEAR EVOLUTION SHOULD TAKE PLACE...CHARACTERIZED BY SWWD BACKBUILDING WITH TIME. EMBEDDED SUPERCELLS/BOWS WILL POSE RISK OF BOTH DAMAGING WIND AND TORNADOES...ALONG WITH HAIL. TRANSITION OF INFLOW PARCELS FROM SFC-BASED TO ELEVATED MAY BE GRADUAL AND NEBULOUS ACROSS DIFFUSE WARM FRONTAL ZONE...SO TORNADO/WIND PROBABILITIES ARE DRAWN TO ALLOW CONSIDERABLE NWD TOLERANCE FOR WARM SECTOR EXPANSION OVER E TX. POTENTIAL FOR RELATIVELY DISCRETE/ROTATING TSTMS WILL BE GREATEST ALONG SWRN/TAIL END OF CONVECTIVE BAND...WHERE BOUNDARY LAYER INFLOW IS MOST UNDISTURBED AND AVAILABLE BUOYANCY RELATIVELY MAXIMIZED. SUCH TSTMS...AS WELL AS ANY RELATIVELY DISCRETE WARM SECTOR CONVECTION...MAY PRODUCE STRONG TORNADOES. EXPECT INFLOW ENVIRONMENT OF RICH MOISTURE...LOW LCL...50-60 KT EFFECTIVE SHEAR...AND VERY LARGE HODOGRAPHS WITH 0-1 KM SRH COMMONLY ABOVE 350 J/KG. MAIN UNCERTAINTIES ATTM INVOLVE INITIATION AND COVERAGE OF ANY SUSTAINED CONVECTION S OF FRONT...AND ALONG OR E OF POSSIBLE DRYLINE. PLUME OF ELEVATED MIXED-LAYER AIR WILL REMAIN OVER MUCH OF THIS REGION THROUGHOUT DAYLIGHT HOURS...ENHANCING LAPSE RATES AND CAPE...BUT ALSO SUPPORTING POTENTIAL FOR CAPPING TO SUPPRESS PREFRONTAL DEVELOPMENT. LATE IN PERIOD...GREATEST SVR POTENTIAL SHOULD SHRINK SEWD IN AREAL EXTENT ACROSS LA...AND DIMINISH SOMEWHAT IN MAGNITUDE...DURING OVERNIGHT HOURS. HOWEVER...DEEP-LAYER SHEAR PROFILES STILL WILL SUPPORT SOME SUPERCELL/BOW POTENTIAL OVER WARM SECTOR. ...W-CENTRAL/NW TX...NW OF ARCTIC FRONT... SCATTERED TSTMS WITH POTENTIAL FOR ISOLATED HAIL SHOULD BE ONGOING AT BEGINNING OF PERIOD ACROSS PORTIONS W-CENTRAL/NW TX. FARTHER W...LEADING EDGE OF STRONGEST MID/UPPER LEVEL ASCENT SHOULD MOVE INTO W-CENTRAL TX AROUND BEGINNING OF PERIOD...BECOMING INCREASINGLY JUXTAPOSED WITH WRN PORTIONS OF ELEVATED WAA AND MOIST ADVECTION REGIME IN LOW LEVELS. THIS SHOULD RESULT IN ADDITIONAL TSTMS IN GENERALLY N-S ALIGNED BAND...SHIFTING EWD ACROSS THIS REGION. FAVORABLE LAPSE RATES AND LOW LEVEL THETAE WILL EXIST TO SUPPORT SOME MUCAPE VALUES 500-1000 J/KG...AMIDST FAVORABLE EFFECTIVE SHEAR FOR ORGANIZED CONVECTION. ALTHOUGH LINEAR MODE SHOULD PREDOMINATE...HAIL MAY OCCUR FROM SOME OF THIS ACTIVITY. ...ARKLATEX REGION... NRN SEGMENT OF FRONTAL CONVECTIVE BAND -- N OF MARINE BOUNDARY -- MAY PRODUCE LARGE HAIL AND STG GUSTS AS IT MOVES INTO SLIGHTLY ELEVATED PLUME OF FAVORABLE BUOYANCY OVER SERN OK...SRN AR...PORTIONS NRN/NERN LA AND EXTREME NE TX. ALTHOUGH LAPSE RATES ALOFT MAY BE WEAKER THAN FARTHER W...RICH LOW LEVEL MOISTURE SHOULD CONTRIBUTE TO MUCAPES UP TO 1000 J/KG...WITH 45-55 KT EFFECTIVE SHEAR. ..EDWARDS/HURLBUT.. 02/16/2008 CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z