MESO: Mesoscale Discussion 1809

ACUS11 KWNS 251013
SWOMCD
SPC MCD 251012
MDZ000-VAZ000-NCZ000-251245-

MESOSCALE DISCUSSION 1809
NWS STORM PREDICTION CENTER NORMAN OK
0512 AM CDT SAT AUG 25 2012

AREAS AFFECTED...PORTIONS SERN VA...EXTREME ERN NC.

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 251012Z - 251245Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...THOUGH MRGL...POTENTIAL IS INCREASING FOR SMALL SUPERCELLS
OVER THIS REGION...AND A SHORT-LIVED TORNADO OR BRIEF DAMAGING GUSTS
CANNOT BE RULED OUT.

DISCUSSION...MOISTURE CHANNEL IMAGERY SHOWS WEAK BUT STILL
WELL-DEFINED MID-UPPER CYCLONE MOVING SLOWLY NEWD ACROSS NRN
NC...AND FCST TO COVER MORE OF ERN VA THROUGH MIDDAY. CONVECTIVE
ENHANCEMENT TO RELATED VORTICITY FIELD IS LIKELY GIVEN TRENDS FROM
PREVIOUS DAY...AND ONGOING PATTERN OF INCREASING RADAR REFLECTIVITY
MAGNITUDES...CONVECTIVE COVERAGE...AND COOLING CLOUD TOPS IN IR
IMAGERY. SFC MESOANALYSIS SHOWS MAIN LOW OVER COASTAL NC BETWEEN
MHX-HSE...ATTACHED TO SFC BAROCLINIC ZONE THAT EXTENDS SWD OVER
ATLC. NRN STRETCH OF THAT BOUNDARY...AS OF 10Z...ARCHED FROM LOW
NNWWD NEAR ASJ THEN NEWD TO EWD ACROSS SERN VA AND MOUTH OF
CHESAPEAKE BAY. THIS CORRESPONDS CLOSELY TO SRN PORTION OF BKN LINE
OF TSTMS THAT HAS PRODUCED TRANSIENT SIGNATURES OF LOW-MIDDLE LEVEL
CYCLONIC SHEAR. BOUNDARY SHOULD MOVE NWD 5-10 KT OVER SERN VA.
THOUGH SUBTLE...BAROCLINICITY WITH VA SECTION OF THIS BOUNDARY IN
PARTICULAR SHOULD BE REINFORCED BY THAT CONVECTION. AUTOMATED
MESOANALYSES ALSO INDICATE FIELD OF ENHANCED LOW-LEVEL VORTICITY
NEAR BOUNDARY...N THROUGH NE OF FKN THEN EWD OFF COAST. RELATED
BACKED FLOW WILL ENHANCED LOW-LEVEL HODOGRAPHS...WHILE CONVERGENCE
IN WEAKLY CAPPED ENVIRONMENT MAINTAINS SUITABLE LIFT FOR TSTMS.

MODIFIED RAOBS AND FCST SOUNDINGS SUGGEST VERY MEAGER BUOYANCY
ACROSS THIS REGION...BECAUSE OF WEAK DEEP-LAYER LAPSE RATES COMBINED
WITH TEMPORAL/NOCTURNAL THERMAL MIN INLAND. NONETHELESS...SFC DEW
POINTS 70S F SUPPORT SUFFICIENTLY RICH LOW-LEVEL THETAE TO YIELD
SFC-BASED EFFECTIVE INFLOW PARCELS...AND MLCAPE RANGING FROM AROUND
500 J/KG NEAR NTU TO LESS THAN 100 J/KG ALONG I-95 S RIC. MAIN
LIMITING FACTORS WILL REMAIN LACK OF MORE ROBUST BUOYANCY...AND
MESSY CONVECTIVE MODE...THOUGH EPISODIC/EMBEDDED MESOCYCLONES REMAIN
POSSIBLE. FARTHER SE ACROSS OUTER BANKS REGION...LOW-LEVEL
SHEAR/VORTICITY APPEAR WEAKER UNDER GREATER CAPE...BUT WITH MORE
DISCRETE CONVECTIVE MODE. TORNADO/WIND POTENTIAL THERE IS EVEN MORE
CONDITIONAL/ISOLATED...BUT NONZERO.

..EDWARDS/THOMPSON.. 08/25/2012

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

ATTN...WFO...AKQ...MHX...

LAT...LON 34727641 35867670 36397721 36827742 37537689 38057516
37857542 37137582 37127596 36947599 36077570 35657545
35157552 35227556 35077601 34837634 34727641

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