SPC AC 200600

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 AM CDT Mon Jul 20 2020

   Valid 211200Z - 221200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE UPPER MIDWEST...MID MISSISSIPPI VALLEY INTO THE OHIO VALLEY AND
   MID-ATLANTIC...AND THE CENTRAL HIGH PLAINS...

   ...SUMMARY...
   Isolated strong to severe thunderstorms may occur Tuesday from parts
   of the Upper Midwest, mid Mississippi Valley into the Ohio Valley,
   and Mid-Atlantic, as well as the central High Plains.

   ...Upper Midwest...
   A shortwave trough is forecast to move eastward across the Upper
   Midwest on Tuesday in tandem with a weak surface low. Both low-level
   moisture and diurnal heating should remain rather limited across
   this region, which may temper the overall severe threat. Still,
   enhanced mid-level west-northwesterly flow should combine with weak
   instability to support organized storms along/ahead of a cold front
   Tuesday afternoon. Both an isolated hail and wind threat may be
   realized given the strong effective shear (35-40 kt) that is
   forecast. These storms should weaken with eastward extent into WI
   Tuesday night as they outpace the northward advance of substantial
   low-level moisture. Lack of more robust forecast instability
   precludes higher severe probabilities at this time.

   ...Mid MS Valley into the OH Valley and Mid-Atlantic...
   A mid-level vorticity maximum separate from the Upper Midwest
   shortwave trough should be present over the mid MS Valley at the
   start of the period, along with ongoing and mainly elevated storms.
   This convection may weaken through Tuesday morning as it moves
   eastward, but one or more MCVs may encourage additional storm
   development across the Upper Midwest by Tuesday afternoon. Although
   the mid-level flow is not forecast to be particularly strong across
   this region (generally 20-30 kt), it should be enough to foster
   modest storm organization. Rich low-level moisture is also forecast
   to gradually spread northward through the day, and a corridor of
   moderate to possibly strong destabilization may ultimately develop.
   Damaging winds would probably be the main threat with any loosely
   organized clusters that move east-northeastward across the warm
   sector through early Tuesday evening. Isolated, marginally severe
   hail may also occur across parts of the mid MS Valley and Midwest
   given the degree of forecast instability.

   Farther east over the OH Valley and Mid-Atlantic, the airmass to the
   south of a weak boundary is expected to become moderately to
   strongly unstable. Mid-level flow around the periphery of an upper
   high centered over the Southeast will likely remain modest. Even so,
   there may be just enough flow through mid levels to support
   multicells and small clusters with any storms that can develop
   Tuesday afternoon. Locally strong to damaging winds should be the
   main threat with this activity.

   ...Central High Plains...
   Low-level upslope flow appears likely to occur Tuesday across parts
   of the central High Plains along/near a weak surface boundary.
   Convection that initially forms over the higher terrain should
   spread eastward with modest (20-30 kt) west-northwesterly flow
   present at mid levels. This activity should encounter at least a
   moderately unstable airmass across parts of eastern WY/northeastern
   CO into western NE and vicinity. Although flow through mid levels is
   not forecast to be particularly strong, it will veer with height
   considerably. This veering should support sufficient effective bulk
   shear coupled with the moderate instability to support isolated
   strong to severe storms. Both large hail and severe wind gusts may
   occur. These storms may spread east-southeastward through Tuesday
   evening while still posing some severe threat. With the lack of more
   pronounced large-scale ascent, overall storm coverage remains
   uncertain.

   ..Gleason.. 07/20/2020

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