May 21, 2013 2000 UTC Day 1 Convective Outlook | |||||||||||||
Updated: Tue May 21 20:01:43 UTC 2013 | |||||||||||||
Probabilistic to Categorical Outlook Conversion Table | |||||||||||||
Public Severe Weather Outlook | |||||||||||||
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The SPC is forecasting ...severe thunderstorms expected over parts of the southern plains and arklatex this afternoon and tonight.... Please read the latest public statement about this event. View What is a Watch? clip. |
Categorical Graphic | |||||||||||||
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Probabilistic Tornado Graphic | |||||||||||||
Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point. |
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Probabilistic Damaging Wind Graphic | |||||||||||||
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point. |
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Probabilistic Large Hail Graphic | |||||||||||||
Probability of hail 1" or larger within 25 miles of a point. Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point. |
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SPC AC 211958 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0258 PM CDT TUE MAY 21 2013 VALID 212000Z - 221200Z ...THERE IS A MDT RISK OF SVR TSTMS OVER NORTH CENTRAL AND NERN TX...SERN OK...SRN AR...AND NRN LA... ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SRN PLAINS ACROSS THE TN VALLEY...LOWER GREAT LAKES...AND THE NERN STATES... ...SRN PLAINS INTO THE TN VALLEY... A SERIES OF LINEAR CONVECTIVE SYSTEMS ARE MOVING EWD FROM SERN OK/NORTH CENTRAL TX INTO AR AND KY/TN...IN ADVANCE OF AN UPPER VORTICITY MAX/SHORT WAVE TROUGH LOCATED OVER THE TX PANHANDLE. STRONG DIABATIC HEATING HAS OCCURRED SOUTH OF A CONVECTIVE BOUNDARY ARCING FROM EAST CENTRAL AR ACROSS SRN AR INTO NORTH CENTRAL TX...AND WITH STEEP LAPSE RATES /REF 18Z FWD AND 19Z SHV SPECIAL RAOBS/ IN PLACE COUPLED WITH SURFACE DEW POINTS AROUND 70F...THE ENVIRONMENT HAS BECOME VERY UNSTABLE WITH SBCAPE NEAR 3500 J/KG. VISIBLE IMAGERY SHOWS CLOUD STREETS OVER ERN TX AND LA FEEDING NWD TOWARD THE THERMAL BOUNDARY INDICATING A FAVORABLE MOISTURE TRANSPORT INTO THE AREA. LOW-LEVEL CONVERGENCE IS FOCUSED IN THREE AREAS: 1) NEAR A SURFACE LOW OVER THE METROPLEX...2) ALONG THE COLD FRONT EXTENDING SWWD INTO THE HILL COUNTRY...AND 3) ALONG THE EAST/WEST CONVECTIVE BOUNDARY ACROSS NERN TX/SWRN AR. STORMS ARE EXPECTED TO INTENSIFY THE REMAINDER OF THIS AFTERNOON INTO THE EVENING AS THE UPPER SYSTEM AND SURFACE LOW MOVE EWD...WITH POTENTIAL FOR SUPERCELLS AND BOWING LINE SEGMENTS. 12Z NSSL WRF-ARW AND RECENT HRRR MODELS INDICATE DEVELOPMENT OF LONG-LIVED BOWING QLCS/S MOVING EWD ACROSS NERN TX INTO SRN AR AND NRN LA...AND ENVIRONMENT APPEARS SUPPORTIVE OF THIS EVENT. THUS...WILL MAINTAIN POTENTIAL FOR VERY LARGE HAIL AND SEVERAL TORNADOES /INCLUDING ONE OR TWO STRONG TORNADOES/ ASSOCIATED PRIMARILY WITH ANY SUPERCELLS THAT FORM...ALONG WITH WIDESPREAD SIGNIFICANT WIND DAMAGE GIVEN THE POTENTIAL FOR A PROGRESSIVE BOWING CONVECTIVE SYSTEM TO FORM WITHIN THE NEXT 1-2 HRS. ELSEWHERE FROM THE MID-SOUTH INTO THE TN VALLEY...ADDITIONAL LINEAR CONVECTIVE SYSTEMS OVER ERN AR AND SRN KY/MIDDLE TN ARE LIKELY TO PROGRESS EWD/NEWD OVER THE NEXT SEVERAL HOURS...WHILE NEW STRONG/SEVERE STORMS HAVE DEVELOPED ALONG THE TRAILING OUTFLOW BOUNDARY OVER FAR NRN MS. GIVEN THE DEGREE OF INSTABILITY WITH CAPE OF 2000-3000 J/KG AND DEEP LAYER SHEAR OF 30-40 KT...A THREAT FOR DAMAGING WINDS AND HAIL WILL CONTINUE WITH THESE STORMS. ..WEISS.. 05/21/2013 .PREV DISCUSSION... /ISSUED 1128 AM CDT TUE MAY 21 2013/ ...SUBSTANTIAL SEVERE WEATHER EXPECTED ACROSS N-CNTRL TX TO THE ARKLATEX THIS AFTERNOON AND EVENING... ..SRN PLAINS TO LOWER MS VALLEY... SIGNIFICANT SEVERE WEATHER EPISODE INITIALLY UNFOLDING ACROSS THE RED RIVER WITH SUPERCELLS PRODUCING LARGE HAIL ALONG AND N OF THE COMPOSITE OUTFLOW/COLD FRONT PUSHING SWD FROM THE BIG COUNTRY TO FAR SERN OK AHEAD OF A WELL-DEFINED SHORTWAVE TROUGH OVER THE SRN HIGH PLAINS. AIR MASS S OF THE BOUNDARY IS BECOMING STRONGLY UNSTABLE AS GRADUAL SURFACE HEATING CONTINUES AMIDST LOWEST 100 MB MEAN MIXING RATIOS OF 14-17 G/KG AND 700-500 MB LAPSE RATES OF 8 TO 9.5 DEG C/KM SAMPLED IN ALL REGIONAL 12Z RAOBS. AS MLCIN IS MINIMIZED ALONG THE DRYLINE MIXING EWD ACROSS THE EDWARDS PLATEAU...ADDITIONAL SUPERCELL DEVELOPMENT IS ANTICIPATED WITH SWD EXTENT. A BELT OF 50-60 KT MID-LEVEL SWLYS ATTENDANT TO THE COMPACT SHORTWAVE TROUGH WILL PROMOTE RISKS FOR ALL SEVERE TYPES /SOME OF WHICH WILL BE SIGNIFICANT/. MORNING CONVECTION-ALLOWING WRF AND HRRR SIMULATIONS ARE INSISTENT THAT UPSCALE GROWTH WILL OCCUR THROUGHOUT THE AFTERNOON. GIVEN THE DEGREE OF INSTABILITY...BUOYANCY AND SHEAR...SETUP MAY YIELD A DERECHO ACCELERATING EWD TOWARDS THE ARKLATEX REGION BY EARLY EVENING. HERE TOO...THE STRONGEST LOW-LEVEL S/SWLYS WILL REMAIN...PROMOTING EMBEDDED MESOVORTICES CAPABLE OF PRODUCING A COUPLE OF SIGNIFICANT TORNADOES. OTHERWISE...POTENTIAL DOES EXIST FOR WIDESPREAD/DESTRUCTIVE DAMAGING WIND GUSTS. ...TN VALLEY TO THE LOWER GREAT LAKES/NORTHEAST... A BROAD AREA OF ORGANIZED SEVERE POTENTIAL IS EXPECTED ALONG THE ERN EXTENT OF THE ELEVATED MIXED LAYER PLUME SAMPLED IN 12Z RAOBS. WITH ROBUST HEATING...MODERATE TO STRONG INSTABILITY IS ANTICIPATED...BUT MOST OF THE REGION WILL REMAIN ON THE FRINGE OF SUFFICIENT DEEP-LAYER SHEAR FOR SUPERCELLS. THREE ZONES OF FOCUS FOR SUSTAINED CONVECTION ARE APPARENT. ONE WILL BE DOWNSTREAM OF AN ONGOING CLUSTER ACROSS WRN TN. THE OTHERS SHOULD BE ALONG A QUASI-STATIONARY FRONT BISECTING NY INTO SRN NEW ENGLAND AND PERHAPS IN ASSOCIATION WITH A WEAK MCV MOVING INTO LOWER MI. MULTICELL CLUSTERS AND A FEW SUPERCELLS WILL BE PRIMARILY CAPABLE OF ISOLATED DAMAGING WINDS AND SEVERE HAIL. CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z |