SPC AC 080553

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1253 AM CDT Wed Jul 08 2020

   Valid 091200Z - 101200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
   THE UPPER MIDWEST AND ACROSS THE CENTRAL PLAINS...

   ...SUMMARY...
   Severe thunderstorms are possible across portions of the Upper
   Midwest and Central Plains on Thursday.

   ...Synopsis...
   A shortwave trough is forecast to be centered over southern Manitoba
   early Thursday. This shortwave is expected to continue eastward into
   western Ontario while another shortwave trough moves quickly through
   the Pacific Northwest and northern Rockies. Upper ridging centered
   over the Southwest is expected to build northward and eastward
   throughout the day. A belt of stronger flow aloft will exist
   throughout the northern periphery of this upper ridge, from northern
   CA eastward through the northern and central Plains. 

   Much of the central and eastern CONUS will be characterized by warm,
   moist, and unstable conditions. However, these conditions will be
   displaced south and east of the stronger synoptic systems.
   Consequently, the severe-weather risk will be largely tied to the
   strength and evolution of antecedent thunderstorms and/or their
   outflow boundaries. Even with the forecast uncertainties inherent
   with this type of pattern, enough consensus exists within the
   guidance (including the available convective-allowing guidance) to
   include 15% wind/hail probabilities over portions of the central
   Plains as well as over the Upper MS Valley. 

   ...Upper MS Valley...
   Convectively induced vorticity maximum will likely emanate from
   overnight storms across SD. Scattered to widespread thunderstorm
   development is anticipated ahead of this vorticity maximum as it
   moves eastward into the warm, moist, and unstable conditions over
   the region Thursday afternoon. Vertical shear across the region is
   generally expected to be weak. However, some localized enhancement
   is possible near the vorticity maximum, aiding the potential for a
   few stronger storms capable of damaging wind gusts and/or isolated
   hail. Cell interactions/mergers could also create updrafts strong
   enough to damaging wind gusts and/or isolated hail.

   ...Central/Southern Plains...
   Severe-weather threat across the central/southern Plains is expected
   to come as a result of two separate linear convective systems. The
   first system is forecast to be ongoing early Thursday morning,
   likely over southeast KS or eastern OK. Some severe threat will
   exist will this system, but it is generally expected to be past the
   mature phase. New storm development is possible along the outflow
   from this system during the afternoon, a few of which could be
   severe. Forecasting where the outflow will be located is difficult,
   evidenced by the broad 5% probabilities from the Ozark Plateau into
   central OK. Increased probabilities will likely be needed whenever
   the location of this outflow becomes more clear.

   Second linear convective system is forecast to develop out of the
   late day thunderstorms that initiate over the central High Plains.
   The overall pattern is favorable for these initially discrete storms
   to grow upscale and proceed downstream across southern NE and
   western/central KS. Hail is the primary threat with the initial
   discrete storms with damaging wind gusts more likely once the storms
   grow upscale.

   ...Carolinas into the Mid-Atlantic...
   A surface low is forecast to be just off the Carolina coast early
   Thursday morning. This low is then expected to move northeastward
   throughout the day. The speed of this movement is uncertain, with
   guidance currently showing a wide spread in where the low will be
   located by 00Z Friday. A more westerly track would potentially bring
   the enhanced southeasterly flow surrounding the system onshore,
   resulting in a low-probability severe risk. Given the uncertainty of
   the overall forecast evolution, no probabilities will be included
   with this outlook. However, probabilities may be needed in later
   outlooks if a more westerly track of the low appears probable.

   ..Mosier.. 07/08/2020

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