000
ACUS01 KWNS 211630
SWODY1
SPC AC 211628

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1128 AM CDT TUE MAY 21 2013

VALID 211630Z - 221200Z

...THERE IS A MDT RISK OF SVR TSTMS FOR N-CNTRL/NERN TX...SRN
AR...NWRN LA...FAR SERN OK...

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SRN PLAINS TO THE
TN/OH VALLEYS AND THE LOWER GREAT LAKES/NORTHEAST...

...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.

..GRAMS/ROGERS.. 05/21/2013