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