[BNAWX] Severe Storm Outlook Narrative

[EMWIN Server]

ACUS11 KWNS 122029
SWOMCD
SPC MCD 122028
VAZ000-NCZ000-SCZ000-WVZ000-TNZ000-GAZ000-122230-

MESOSCALE DISCUSSION 0763
NWS STORM PREDICTION CENTER NORMAN OK
0328 PM CDT THU MAY 12 2011

AREAS AFFECTED...SRN WV...WRN VA...FAR NERN TN...WRN/CNTRL NC...MUCH
OF SC...FAR NERN GA

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 122028Z - 122230Z

ISOLATED SVR TSTMS WITH LARGE HAIL AND DMGG WINDS WILL BE POSSIBLE
THROUGH LATE AFTERNOON ACROSS SRN PORTIONS OF THE APPALACHIANS AND
ADJACENT AREAS OF THE MIDDLE ATLANTIC AND SOUTHEAST.

MID-AFTERNOON SFC ANALYSIS REVEALS A STATIONARY FRONT EXTENDING FROM
NWRN WV SSEWD INTO ERN SC. AN EXPANSIVE STRATUS DECK TO THE EAST OF
THIS BOUNDARY IS YIELDING AMPLE CINH FOR SFC-BASED PARCELS...WHILE
AT LEAST POCKETS OF INSOLATION WEST OF THE BOUNDARY AMIDST SFC
DEWPOINTS IN THE 60S HAVE YIELDED A MODERATELY UNSTABLE AIR MASS
WITH MLCAPE VALUES OF 1000-2000 J/KG. UPSLOPE FLOW INVOF THE BLUE
RIDGE HAS RESULTED IN THE RECENT INITIATION OF DEEP CONVECTION OVER
WRN PORTIONS OF NC. MEANWHILE...ASCENT ASSOCIATED WITH A WEAK
MID-LEVEL IMPULSE CRESTING THE ERN CONUS RIDGE HAS SUPPORTED THE
DEVELOPMENT OF CONVECTION FARTHER NORTH INTO SRN WV AND WRN VA. ALL
OF THIS ACTIVITY WILL CONTINUE TO BE STEERED SSEWD THROUGH THE
AFTERNOON...WITH ADDITIONAL DEVELOPMENT EXPECTED OVER HIGHER TERRAIN
AND INVOF THE FRONT.

TWO SEPARATE SPATIAL REGIMES FOR ISOLATED SVR CONVECTION WILL EXIST:

1. TO THE WEST OF THE FRONT...A PRIMARILY MULTICELLULAR CONVECTIVE
MODE WILL BE FAVORED WITH SURFACE-BASED CONVECTION...GIVEN THAT THE
STRONGEST MID-LEVEL FLOW IS DISPLACED FARTHER TO THE EAST. THIS WILL
LIKELY MITIGATE THE OVERALL THREAT FOR STORM PERSISTENCE/SUSTENANCE.
ISOLATED INCIDENTS OF LARGE HAIL WILL BE POSSIBLE GIVEN THE DEGREE
OF UPWARD BUOYANCY...WITH AN ESTIMATE OF PENNY SIZE HAIL ALREADY
REPORTED IN HENDERSON COUNTY NC. SFC TEMPERATURE-DEWPOINT SPREADS IN
EXCESS OF 15-20F IN MANY AREAS COULD ALSO YIELD A THREAT FOR DMGG
WINDS.

2. TO THE EAST OF THE FRONT...CONVECTION WILL BE ROOTED ATOP A
STABLE LAYER...WITH AN ISOLATED THREAT FOR LARGE HAIL. THE ABSENCE
OF ANY APPRECIABLE SFC-BASED INSTABILITY AND THE WEAK NATURE OF THE
MID-LEVEL IMPULSE WILL MITIGATE THE SVR THREAT.

GIVEN THE LIMITED SPATIAL EXTENT OF ANY SVR THREAT...THE ISSUANCE OF
A WW IS UNLIKELY.

..COHEN.. 05/12/2011

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...RAH...ILM...RNK...RLX...CAE...GSP...MRX...

LAT...LON   37668168 37808043 37527985 37157941 36767922 36057914
            35167939 34447960 33648012 33188079 33408185 34858338
            36418311 37668168


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