SPC MD 1356



MD 1356 CONCERNING SEVERE POTENTIAL…WATCH UNLIKELY FOR PORTIONS OF NEW ENGLAND

MD 1356 Image


Mesoscale Discussion 1356
NWS Storm Prediction Center Norman OK
1220 PM CDT Thu Jul 30 2020

Areas affected...portions of New England

Concerning...Severe potential...Watch unlikely 

Valid 301720Z - 301915Z

Probability of Watch Issuance...20 percent

SUMMARY...Developing thunderstorms ahead of a diffuse frontal zone
may pose a risk for damaging winds this afternoon. There is
considerable uncertainty on storm coverage/evolution, and the
potential need for weather watch.

DISCUSSION...Morning upper-air analysis showed a broad cyclonic
trough over eastern Canada and the northeastern US with a belt of
stronger (45-55 kt) mid-level westerly flow rounding the base of the
trough. A diffuse frontal zone was located roughly northeast to
southwest through much of New England and the Northeast. In the
vicinity of the frontal zone, isolated thunderstorms have developed,
and additional storms are likely to develop over the next few hours.
Thermodynamics are only marginally supportive of robust convection
given poor mid-level lapse rates and around 500-750 J/kg of MLCAPE.
However, effective vertical shear around 50 kt, from the ribbon of
stronger flow aloft, should support robust, albeit lower topped
storms despite the marginal buoyancy. Isolated storms in the form of
multi-cell clusters/line segments, and occasional supercells will
pose a threat for damaging wind gusts given the strength of
background flow aloft, and low-level thermo profiles favoring
downdraft acceleration.

There remains much uncertainty on the amount of storm coverage this
afternoon. The lack of better defined forcing along the diffuse
frontal zone suggests storm development will be possible over a
relatively broad area. CAM guidance has struggled to capture
currently ongoing storms lending little credibility to forecast
guidance. Thus, while not overly likely given the relatively poor
thermodynamics, a weather watch may be necessary should storm
coverage increase given the potential for damaging wind gusts.

..Lyons/Goss.. 07/30/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...GYX...BOX...BTV...OKX...ALY...PHI...BGM...CTP...

LAT...LON   41297098 40947203 40457400 40027536 40247645 40817711
            41047731 41667678 42927489 43367417 44037354 44177343
            43647142 43077072 42217037 41467064 41297098 

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