DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 211959
SWODY1
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.

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