MESO: Mesoscale Discussion 1249

ACUS11 KWNS 261902
SWOMCD
SPC MCD 261902
MAZ000-RIZ000-CTZ000-262130-

MESOSCALE DISCUSSION 1249
NWS STORM PREDICTION CENTER NORMAN OK
0202 PM CDT WED JUN 26 2013

AREAS AFFECTED...A LARGE PART OF MA...PARTS OF NRN/ERN CT...RI

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 261902Z - 262130Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...THE AREA IS BEING MONITORED FOR INCREASING SVR POTENTIAL
AND THE POSSIBLE ISSUANCE OF A SVR THUNDERSTORM WATCH THIS
AFTERNOON.

DISCUSSION...ACROSS THE MCD AREA...A POCKET OF PARTLY CLOUDY TO
MOSTLY SUNNY SKIES LIES BETWEEN HIGHER-DENSITY/OPAQUE MULTI-LAYERED
CLOUDS STREAMING ACROSS CNTRL/NRN NEW ENGLAND...AND AN EWD-EXTENDING
PLUME OF SIMILAR CLOUDS MOVING ESEWD ACROSS SERN NY AND SRN CT INTO
THE ADJACENT WRN ATLANTIC. SFC DIABATIC HEATING ACROSS THIS POCKET
OF ENHANCED ISOLATION AMIDST MIDDLE 60S SFC DEWPOINTS IS
CONTRIBUTING TO AROUND 1000-1500 J/KG OF MLCAPE PER MODIFIED 12Z
RAOBS AND FORECAST SOUNDINGS. FURTHER DESTABILIZATION WILL BE
CONTRIBUTED BY /1/ CONTINUED STEEPENING OF LOW-LEVEL LAPSE RATES
THROUGH THE AFTERNOON...AND /2/ INCREASING LARGE-SCALE UPWARD MOTION
PRECEDING A MID-LEVEL SHORTWAVE TROUGH APPROACHING FROM THE GREAT
LAKES REGION. THUNDERSTORMS WILL LIKELY INCREASE IN NUMBER/INTENSITY
THROUGH THE AFTERNOON AMIDST THE MODERATE INSTABILITY AS LOW-LEVEL
ASCENT ALONG THE FRINGES OF THE MULTI-LAYERED CLOUDS/DIFFERENTIAL
HEATING ZONES IS AUGMENTED BY INLAND-MOVING SEA BREEZE CIRCULATIONS.

BOX VWP DATA INDICATE AROUND 30 KT OF FLOW IN THE 3-5-KM-AGL
LAYER...AND SOME INCREASE IN MID-LEVEL FLOW MAY OCCUR AS THE HEIGHT
GRADIENT TIGHTENS IN ASSOCIATION WITH THE APPROACH OF THE SHORTWAVE
TROUGH. CORRESPONDING MODERATE DEEP SHEAR MAY SUPPORT ORGANIZED
STORM STRUCTURES INCLUDING MULTICELLS AND PERHAPS MARGINAL SUPERCELL
STRUCTURES...WITH THE POTENTIAL FOR DMGG WINDS AND SVR HAIL.
HOWEVER...MID-LEVEL LAPSE RATES ARE NOT PARTICULARLY STEEP...AND THE
STRONGEST DEEP-LAYER FORCING FOR ASCENT COULD REMAIN DISPLACED TO
THE W OF THE AREA THROUGH PEAK HEATING. THESE FACTORS BREED
UNCERTAINTY REGARDING THE ANTICIPATED CONVECTIVE INTENSITY...THOUGH
THE AREA WILL BE MONITORED FOR THE POSSIBLE ISSUANCE OF A SVR
THUNDERSTORM WATCH THROUGH THE AFTERNOON.

..COHEN/KERR.. 06/26/2013

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

ATTN...WFO...BOX...OKX...ALY...

LAT...LON 41247134 41797300 42307316 42597244 42647061 42317015
41766985 41146996 41247134

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