MESO: Mesoscale Discussion 1753

ACUS11 KWNS 221803
SWOMCD
SPC MCD 221803
NHZ000-VTZ000-MAZ000-NYZ000-NJZ000-PAZ000-222030-

MESOSCALE DISCUSSION 1753
NWS STORM PREDICTION CENTER NORMAN OK
0103 PM CDT THU AUG 22 2013

AREAS AFFECTED...PORTIONS OF PA...NY...VT...WRN NH...WRN MA

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 221803Z - 222030Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...A BROAD AREA OF ISOLATED...MARGINAL SEVERE THUNDERSTORM
POTENTIAL WILL EXIST THROUGH THIS AFTERNOON. WHILE TRENDS WILL
CONTINUE TO BE MONITORED...THE ISSUANCE OF A WW IS CURRENTLY
UNLIKELY.

DISCUSSION...VISIBLE SATELLITE LOOPS INDICATE THE CU FIELD BECOMING
INCREASINGLY AGITATED ACROSS A BROAD AREA AHEAD OF A FRONT CROSSING
SRN ONTARIO/QUEBEC. AREAS OF INSOLATION ARE SUPPORTING DIABATIC SFC
HEATING AMIDST FAIRLY RICH BOUNDARY-LAYER MOISTURE CHARACTERIZED BY
SFC DEWPOINTS IN THE LOWER/MIDDLE 60S. DESPITE WEAK MID-LEVEL LAPSE
RATES...SFC TEMPERATURES HAVE CLIMBED INTO THE MIDDLE 70S TO LOWER
80S ALLOWING FOR MLCINH TO BE SUFFICIENTLY REDUCED TO SUPPORT
ISOLATED THUNDERSTORM DEVELOPMENT PER RECENT MOSAIC RADAR/LIGHTNING
DATA.

WITH MLCAPE VALUES FORECAST TO HOLD AROUND 500-1500 J/KG THROUGH THE
AFTERNOON OUTSIDE OF AREAS OF CONVECTIVE OVERTURNING...A FEW INTENSE
UPDRAFTS/DOWNDRAFTS WILL LIKELY ENSUE AS CONVECTION INCREASES IN
COVERAGE/INTENSITY OWING TO DIURNALLY DEEPENING PBL AND OROGRAPHIC
CIRCULATIONS. ADDITIONAL ASCENT WILL EMANATE FROM ASCENDING BRANCHES
OF LAKE BREEZE CIRCULATIONS E OF LAKES ONTARIO AND ERIE...AND AROUND
DIFFERENTIAL-HEATING INDUCED BAROCLINICITY ALONG FRINGES OF
MULTI-LAYERED CLOUD DECKS FROM NRN NY INTO NRN VT/NH. ISOLATED
MARGINALLY SVR WIND/HAIL CANNOT BE RULED OUT WITH THE MOST INTENSE
CONVECTION THAT COULD LOCALLY/OCCASIONALLY ORGANIZE INTO SMALL
CLUSTERS/LEWP SEGMENTS.

HOWEVER...WATER VAPOR LOOPS SUGGEST THAT MORE PROMINENT MID-LEVEL
PERTURBATIONS AND ACCOMPANYING STRONGER DEEP ASCENT WILL REMAIN
DISPLACED TO THE N OF THE DISCUSSION AREA THROUGH THE AFTERNOON/PEAK
OF DIURNAL HEATING...WITH EFFECTIVE BULK SHEAR MAGNITUDES EXPECTED
TO REMAIN GENERALLY 25 KT OR LESS. THE LACK OF OVERLAP OF THE
AFOREMENTIONED BUOYANCY WITH STRONGER VERTICAL SHEAR NEAR THE
FRONTAL ZONE SHOULD PREVENT A MORE ORGANIZED/WIDESPREAD SVR THREAT
FROM EVOLVING. HOWEVER...THERE IS SOME CONCERN THAT STRENGTHENING
LOWER/MIDDLE TROPOSPHERIC FLOW MAY OCCUR ACROSS NRN NY INTO NRN
VT/NH LATER THIS AFTERNOON AS THE FRONT ENTERS THE AREA FROM THE N.
WHILE TRENDS WILL BE MONITORED...IT CURRENTLY APPEARS THAT
STABILIZATION OWING TO PRE-FRONTAL CLOUDS/PRECIPITATION MAY PROVE
DELETERIOUS IN MAINTAINING A MORE ROBUST CONVECTIVE THREAT IN
ASSOCIATION WITH THE SFC FRONT LATER TODAY.

..COHEN/CORFIDI.. 08/22/2013

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

ATTN...WFO...GYX...BOX...BTV...OKX...ALY...PHI...BGM...BUF...
CTP...PBZ...CLE...

LAT...LON 40388008 41747978 43177783 44537566 44917471 45047343
44987187 44497142 42877257 41297478 40217713 40388008

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