SPC AC 090730

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0230 AM CDT Thu Jul 09 2020

   Valid 111200Z - 121200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF THE SOUTHERN PLAINS AND OZARK PLATEAU...AND OVER THE COASTAL
   MID-ATLANTIC AND NEW ENGLAND...

   ...SUMMARY...
   Isolated severe thunderstorms are possible across portions of the
   southern Plains and Ozark Plateau on Saturday. A few strong storms
   are also possible over the coastal Mid-Atlantic and New England.

   ...Synopsis...
   Upper ridging will remain in place over the Southwest, with some
   westward expansion into the Great Basin and southern/central CA
   anticipated. Farther north, a shortwave trough is forecast to move
   from the Upper Midwest and into the Upper Great Lakes/Mid MS Valley 
   while another shortwave trough moves through the Pacific
   Northwest/British Columbia late. Over the eastern CONUS, broad upper
   troughing will likely extend from the Upper Great Lakes into the
   southern Appalachians at the beginning of the period. This upper
   trough is then forecast to gradually move eastward throughout the
   day. Additionally, a surface low (and attendant mid-level cyclone)
   will be over and approaching southern New England early Saturday
   morning, with a generally northward track expected during the
   period.

   ...Southern Plains/Ozark Plateau...
   Decaying MCS may be ongoing over eastern KS/southwest MO/northeast
   OK at the beginning of the period, with at least some downstream
   severe potential possible. Greater severe potential is anticipated
   later in the day along any residual outflow from this MCS. Air mass
   over the region will be very warm and moist, contributing to strong
   instability. This region is expected to be on the edge of the
   stronger northwesterly flow aloft but enough vertical shear will
   likely be in place to support severe storms. This severe potential
   will rely on the existence of a mesoscale boundary, which has
   limited predictability at this forecast range. The overall parameter
   space looks very favorable for severe but the limited predictability
   merits only introducing a 5% probability with this outlook.

   ...Northern Mid-Atlantic into New England...
   Position of the surface low (and related mid-level cyclone) will
   critical for determined the areas of greatest severe risk across the
   region Saturday. Overall expectation is for enhanced low to
   mid-level winds to be in place east of the surface low, coincident
   with modest instability. Unfortunately, model guidance does not
   currently have a good consensus on the location of this low, which
   limits predictability and precludes anything higher than 5% severe
   probabilities. With that being said, a large 5% area was delineated
   from NJ northeastward into southern ME where at least some severe
   threat is currently indicated by the guidance. Refinements to this
   area are likely in later outlooks as position and track of the
   surface low become more predictable.

   ...Mid-Atlantic...
   Widespread thunderstorms are expected over the Mid-Atlantic ahead of
   the broad upper trough (and its attendant surface trough). Moderate
   instability will likely be in place but weak vertical shear is
   expected to limit storm organization/updraft persistence, tempering
   the overall severe potential.

   ..Mosier.. 07/09/2020

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