SPC AC 110554

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1254 AM CDT Sat Jul 11 2020

   Valid 121200Z - 131200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE LOWER
   MISSISSIPPI VALLEY TO THE OHIO VALLEY AND CENTRAL APPALACHIANS...AS
   WELL AS OVER THE CENTRAL/SOUTHERN HIGH PLAINS...

   ...SUMMARY...
   Isolated severe thunderstorms will be possible on Sunday across
   portions of the southern U.S. into the Ohio Valley and central
   Appalachians vicinity, as well as across parts of the central and
   southern High Plains. Locally damaging winds and hail will be the
   main hazard with storms through Sunday evening.

   ...Lower MS Valley into the Ohio Valley and Central Appalachians
   Vicinity...

   Convection may be ongoing Sunday morning across portions of the
   Lower OH Valley toward AR. The impact this convection has on overall
   severe threat in the Day 2 period remains uncertain, as much
   uncertainty in convective evolution during the Day 1/Sat period
   remains. Nevertheless, an upper trough will be oriented
   north-to-south from Lake Erie toward the Southeast, with modest
   northwesterly deep layer flow persisting over the region. A weak
   surface low is forecast to migrate eastward from IL/IN early Sunday
   morning toward eastern KY by Sunday night, with a trailing cool
   front dropping southeast across the Midwest into the Mid-South/TN
   Valley vicinity. Deep layer flow will largely remain veered, leading
   to weak directional shear, but modestly increasing speeds with
   height should allow for sufficient effective shear to aid in
   clusters of semi-organized convection. A very moist boundary layer
   and strong heating will result in moderate instability, with MLCAPE
   values from around 1000-2000 J/kg (locally higher) and steepening
   low level lapse rates will enhance localized areas of damaging wind
   potential. Midlevel lapse rates will generally be less than 7 C/km
   across the region, but a few of the strongest cells could produce
   marginally severe hail, mainly from the lower OH Valley into the
   South. 

   Depending where any MCVs or boundaries associated with convection in
   the Day 1 period become located by Sunday morning, a corridor or two
   of greater severe risk could materialize. However, uncertainty is
   still too high to introduce Slight risk probabilities at this time. 


   ...Central/Southern High Plains Vicinity...

   An intense upper high will be centered over NM, with an associated
   ridge extending northward through the northern High Plains. Warm
   midlevel temperatures will result in capping for much of the period,
   limiting thunderstorm potential. However, an upper shortwave trough
   is forecast to shift east/southeast across the northern Rockies,
   bringing a belt of stronger west/northwesterly flow across the
   Rockies. Southeasterly low level flow will transport modest boundary
   layer moisture northward across the Plains, with upper 50s to low
   60s F surface dewpoints forecast across much of the High Plains. An
   area of somewhat higher dewpoints is possible from the OK/TX
   Panhandle vicinity into parts of northeast NM and eastern CO.
   Thunderstorms are expected to develop during the afternoon over
   higher terrain, and spread eastward over lower elevations of eastern
   CO/northeast NM. This high-based convection could pose a threat for
   isolated damaging gusts in a narrow corridor east of the mountains
   into the evening hours where forecast guidance suggests increasing
   moisture and height falls associated with the approaching trough
   should erode the cap. This activity should quickly diminish with
   eastward extent during the evening hours as inhibition once again
   increases.

   ..Leitman.. 07/11/2020

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