MESO: Mesoscale Discussion 1741

ACUS11 KWNS 211726
SWOMCD
SPC MCD 211726
NCZ000-WVZ000-VAZ000-SCZ000-OHZ000-TNZ000-KYZ000-212000-

MESOSCALE DISCUSSION 1741
NWS STORM PREDICTION CENTER NORMAN OK
1226 PM CDT WED AUG 21 2013

AREAS AFFECTED...PORTIONS OF SRN OH...ERN KY...ERN
TN...SRN/WRN/CNTRL WV...WRN VA...WRN NC...WRN SC

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 211726Z - 212000Z

PROBABILITY OF WATCH ISSUANCE...5 PERCENT

SUMMARY...A BROAD AREA OF STRONG THUNDERSTORM POTENTIAL WILL EXIST
FROM PARTS OF THE OHIO RIVER VALLEY TO THE CNTRL/SRN APPALACHIANS
AND ADJACENT LOWER ELEVATIONS THIS AFTERNOON. AN ISOLATED MARGINAL
SVR THUNDERSTORM POTENTIAL CANNOT BE RULED OUT.

DISCUSSION...FAIRLY RICH TROPOSPHERIC MOISTURE EXISTS ACROSS THE
AREA...WITH 1.5-1.7-INCH PW VALUES PER GPS DATA...ALONG WITH SFC
DEWPOINTS IN THE UPPER 60S TO LOWER 70S. POCKETS OF AT LEAST
FILTERED SUNSHINE ARE CONTRIBUTING TO GENERALLY MODERATE TO LOCALLY
STRONG INSTABILITY ACROSS THE REGION...WITH SFC TEMPERATURES HAVING
INCREASED INTO THE MIDDLE 70S TO LOWER 80S. MODIFICATIONS TO THE 12Z
RAOBS FROM WILMINGTON OHIO AND NASHVILLE TENNESSEE SUGGEST MLCAPE
VALUES EXCEEDING 2000 J/KG ACROSS PORTIONS OF KY AND ADJACENT
TN/OH/WV IN AREAS OF GREATER INSOLATION. DESTABILIZATION IS ALSO
BEING CONTRIBUTED BY THE INFLUENCE OF DCVA/MID-LEVEL ASCENT
PRECEDING A CYCLONE THAT IS APPROACHING SWRN OHIO FROM THE W PER
WATER VAPOR DATA.

FORCING FOR ASCENT PRECEDING THE CYCLONE...ALONG WITH DIURNALLY
DEEPENING PBL AND OROGRAPHIC CIRCULATIONS AMIDST WEAK MLCINH AND
OUTFLOW BOUNDARIES...SHOULD FOSTER A CONTINUED UPTICK IN THE
COVERAGE/INTENSITY OF STORMS DURING THE NEXT FEW HOURS. VWP DATA
ACROSS THE MCD AREA SAMPLE A BAND OF 20-40-KT MID-LEVEL FLOW IN
ASSOCIATION WITH A TIGHTER HEIGHT GRADIENT SE OF THE CYCLONE --
STRONGEST IN CLOSER PROXIMITY TO THE CYCLONE PER JKL VWP.
CORRESPONDING ENHANCED DEEP SHEAR SHOULD SUPPORT A FEW LOOSELY
ORGANIZED CONVECTIVE STRUCTURES THAT MAY PRODUCE STRONG SFC GUSTS
AND SMALL HAIL...AND AN ISOLATED MARGINAL SVR THUNDERSTORM POTENTIAL
COULD EVOLVE WITH THE MOST INTENSE/SUSTAINED STORMS. SUCH POTENTIAL
/ALBEIT LIMITED/ WILL BE MAXIMIZED IN AREAS OF GREATER ANTECEDENT
SFC DIABATIC HEATING -- I.E. ACROSS ERN KY...WRN WV...AND SRN OH.
LIMITED SPATIAL PHASING BETWEEN STEEPER MID-LEVEL LAPSE RATES NEAR
THE CYCLONE AND ZONE OF ENHANCED DEEP SHEAR SHOULD MITIGATE THE
OVERALL SVR POTENTIAL.

..COHEN/CORFIDI.. 08/21/2013

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

ATTN...WFO...RAH...RNK...RLX...CAE...GSP...MRX...JKL...ILN...
LMK...OHX...

LAT...LON 36028626 38988350 39348188 38888056 37298031 35088023
34218146 34378251 35518234 35798318 35368443 35328560
36028626

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