SWOMCD
SPC MCD 301739
NCZ000-VAZ000-SCZ000-302015-
MESOSCALE DISCUSSION 2219
NWS STORM PREDICTION CENTER NORMAN OK
1239 PM CDT FRI SEP 30 2011
AREAS AFFECTED...PORTIONS CENTRAL-ERN NC...SERN VA.
CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
VALID 301739Z - 302015Z
TSTMS FCST TO DEVELOP BEGINNING NEXT 1-2 HOURS AND INCREASE N
COVERAGE THROUGH MID-LATE AFTERNOON OVER DISCUSSION AREA. SVR GUST
POTENTIAL MAY DEVELOP IN STEP WITH THAT INCREASE IN COVERAGE...AND
ALSO...STRENGTHENING DEEP-LAYER SPEED SHEAR RELATED TO APCH OF
MID-UPPER TROUGH.
VIS IMAGERY SHOWS BANDS OF DEEP CU AND TCU DEVELOPING OVER COASTAL
PLAIN. IN THAT CORRIDOR...BOUNDARY LAYER IS RELATIVELY DEEP AND
RICH IN LOW-LEVEL MOISTURE COMPARED TO FARTHER W. ALTHOUGH
CONVERGENCE ON SCALE OF AVAILABLE OBS APPEARS WEAK...GIVEN ONLY 5-10
KT SFC FLOW AT MOST SITES...EXPECT ISOLATED THEN WIDELY SCATTERED
TSTM DEVELOPMENT FROM COMBINATION OF
1. WEAKENING MLCINH...PER MODIFIED MHX RAOB AND RUC SOUNDINGS...AND
2. LOCALIZED/SUB-OBSERVATIONAL SCALE SOURCES OF LOW-LEVEL LIFT INVOF
SEA BREEZES AND HORIZONTAL CONVECTIVE ROLLS.
THIS EARLY CONVECTION INITIALLY SHOULD RESIDE E OF MOST FAVORABLE
SHEAR...THOUGH ISOLATED...PRECIP LOADING-DRIVEN DOWNBURST NEAR SVR
LEVELS CANNOT BE RULED OUT.
POTENTIAL FOR TSTMS ALSO WILL INCREASE IN SECOND AND SOMEWHAT
OVERLAPPING PHASE AROUND 19Z-22Z OVER PIEDMONT REGION AS LEADING
EDGE OF DCVA PLUME IMPINGES ON WARM SECTOR AND STEEPENS LOW-MIDLEVEL
LAPSE RATES. STRONGEST MIDLEVEL ASCENT CURRENTLY IS BEHIND DIFFUSE
SFC COLD FRONT THAT IS ANALYZED FROM CENTRAL MD SWWD OVER W-CENTRAL
NC AND W-CENTRAL SC. HOWEVER...CONTINUED SFC HEATING AND WEAKENING
CINH WILL RESULT IN SWATH OF MLCAPE 1000-1500 J/KG JUST E OF COLD
FRONT OVER CENTRAL NC AND 1500-2000 J/KG NEAR COAST...DECREASING
NEWD INTO SERN VA BUT STILL BECOMING FAVORABLE FOR TSTMS. ALTHOUGH
LOW-LEVEL HODOGRAPHS AND SHEAR WILL REMAIN SMALL...35-45 KT
EFFECTIVE SHEAR MAGNITUDES--DRIVEN MAINLY BY SPEED SHEAR--WILL
SUPPORT TSTM ORGANIZATION.
..EDWARDS.. 09/30/2011
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...AKQ...MHX...RAH...ILM...RNK...
LAT...LON 34347761 34197814 34417905 34847978 35407993 36637863
37457718 36877612 36037565 35497580 34917641 34347761
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