SPC AC 051735

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1235 PM CDT Sun Jul 05 2020

   Valid 061200Z - 071200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHEAST
   MT...NORTHEAST WY...FAR SOUTHWEST ND AND PORTIONS OF WESTERN/CENTRAL
   SD...

   ...SUMMARY...
   Severe thunderstorms producing large hail and damaging wind gusts
   are possible across portions of the northern High Plains Monday.
   Additional strong to isolated severe storms are possible across the
   middle Missouri Valley and Upper Midwest, as well as across parts of
   the Mid-Atlantic vicinity.

   ...Synopsis...

   An upper ridge will extend northwestern Mexico through the central
   Rockies on Monday. The ridge may meander/expand eastward a bit
   through the period, but overall will not be very progressive.
   Further east, a weak mid/upper trough will progress eastward from
   OK/north TX toward the mid-South/TN Valley vicinity. Widespread
   thunderstorms are expected across much of the south-central into the
   southeast U.S. where a seasonally moist and unstable environment
   will exist beneath the weak trough. A couple of embedded and
   convectively enhanced MCVs could lead to occasional strong storms,
   mainly capable of downburst winds. However, weak vertical shear and
   modest lapse rates will limit any organized severe threat from the
   southern Plains to the southeast states.

   In northern stream flow, an upper trough will dig across northern CA
   and the Pacific northwest, becoming oriented from eastern WA to NV
   by Tuesday morning. This will result in a band of enhanced
   west/southwesterly flow from the northern Great Basin into MT/WY.
   Another, albeit weaker, shortwave trough will migrate across the
   northern Plains and Upper Midwest, topping the upper ridge to the
   south and resulting in increasing west/northwesterly mid/upper level
   flow from the Dakotas eastward to the Upper Midwest. A surface cold
   front draped across the region from central MN south/southwest to
   northeast WY will be a focus for afternoon and evening severe
   thunderstorm development.

   Additional strong to isolated severe storms are possible from
   southern NY southward into northern VA. 

   ...MT/northeast WY into the Upper Midwest...

   Eastern portions of the aforementioned surface cold front will
   progress east/southeast through the afternoon. Ahead of the front,
   surface dewpoints in the mid/upper 60s and modestly steep midlevel
   lapse rates will support MLCAPE values from 1500-2500 J/kg (possibly
   higher) across WI and southern MN southwestward into parts of SD and
   NE. Vertical shear will be rather weak, with some improvement by
   late afternoon/evening. Strong surface heating will result in steep
   low level lapse rates, increasing the risk for strong downburst
   winds as thunderstorms develop ahead of the surface cold front.
   Given weak shear, thunderstorm clusters will be the main convective
   mode, with sporadic strong/locally damaging gusts and hail possible.


   Further west, the cold front will stall and become less defined
   across southern MT/northern WY into western SD. southeasterly low
   level winds atop increasing mid/upper level westerly flow will
   result in strong vertical shear. Surface dewpoints will generally
   range from the mid 50s to low 60s, and development of MLCAPE values
   as high as 2000 J/kg will be aided by steep midlevel lapse rates and
   strong heating. Widely scattered storms are expected by late
   afternoon and stronger shear will result in well-organized, though
   somewhat high-based supercells tracking southeast from southern
   MT/northeastern WY into western SD. Strong, locally damaging winds
   and large hail will be possible with these cells. Some guidance
   suggests one or more bowing segments could develop during the
   evening as a southwesterly low level jet increases. This could
   result in a severe threat persisting into the nighttime hours
   further downstream into parts of central/eastern SD, but confidence
   in this scenario is low and the Slight risk has only been extended a
   bit further east to account for this scenario. 

   ...Southern NY/western PA and the Mid-Atlantic Vicinity...

   Modest vertical shear will exist across the region on Monday
   afternoon/evening, with strong flow and forcing for ascent focused
   further to the north over New England as a shortwave trough shifts
   eastward and eventually offshore. However, a very moist airmass will
   be in place, with surface dewpoints in the 60s to near 70 F common.
   Strong heating (high temps 85-95) will result in steep low level
   lapse rates and MLCAPE values from 2000-3000 J/kg. Midlevel lapse
   rates also will be steeper thanks to cooling aloft associated with
   the aforementioned shortwave trough. As a result, clusters of
   thunderstorms capable of sporadic strong/locally damaging gusts and
   occasional hail will be possible during the afternoon and evening.

   ..Leitman.. 07/05/2020

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