SPC Day 1 Outlook

   SPC AC 070558

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1258 AM CDT Sat Aug 07 2021

   Valid 071200Z - 081200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
   PLAINS TO THE UPPER MISSISSIPPI VALLEY...

   ...SUMMARY...
   Scattered severe storms capable of producing mainly large hail and
   damaging winds gusts will be possible today from parts of the
   northern/central Plains into the upper Mississippi Valley.

   ...Synopsis...
   A mid-level short-wave trough is forecast to shift out of the
   Rockies and into the central and northern Plains today, ahead of a
   stronger trough digging southeastward across western Canada toward
   the northwestern U.S. through the period.  Meanwhile in the East,
   weak mid-level troughing is expected to cross the Appalachians and
   move into the East Coast states.

   At the surface, a cold front will shift into/across the northwestern
   states ahead of the aforementioned/digging upper trough.  Over the
   Plains, a more ill-defined surface pattern is progged -- in part due
   to widespread convection and associated boundary interaction. 
   Generally, a weak synoptic baroclinic zone will extend from the
   upper Mississippi Valley to the southern High Plains -- lingering
   through the period.  

   Elsewhere, high pressure will prevail east of the Mississippi,
   though a very weak surface low/trough will affect the Carolinas
   area, in conjunction with the advance of the weak upper system.

   ...Central Plains and vicinity eastward across the upper Mississippi
   Valley...
   Complex convective evolution is expected across central portions of
   the country today, with multiple areas of storm development/growth
   expected.  Storms will likely be ongoing at the start of the period
   over southern Minnesota/northern Iowa vicinity, and in a more
   isolated manner westward into the Dakotas, and southwestward into
   Kansas.  

   Through the day, as heating contributes to widespread moderate
   destabilization, the Minnesota storm cluster will likely shift into
   Wisconsin, followed by several areas of new storm initiation
   westward and southwestward along the weak surface front, as the
   upper short-wave trough advances into the Plains during the
   afternoon.

   With a belt of enhanced (35-45 kt) low- to mid-level southwesterly
   flow preceding the trough, aligned from the central High
   Plains/Texas Panhandle northeastward to the upper Mississippi
   Valley, sufficient shear for storm organization will exist.  Large
   hail will be possible with stronger updrafts, especially during the
   afternoon as convection remains more cellular in some areas. 
   However, the more substantial severe risk will likely be in the form
   of locally damaging winds, as storms grow upscale into one or more
   clusters during the evening -- within a zone extending from northern
   Kansas/Nebraska to the upper Mississippi Valley region.

   More isolated/higher-based storms -- capable of producing locally
   strong wind gusts -- are expected farther southwestward from western
   Kansas into the Texas Panhandle during the afternoon and early
   evening hours.

   ...Eastern North Carolina/southeastern Virginia area...
   Widespread -- but generally sub-severe -- convection is forecast
   across the North Carolina/Virginia vicinity today, ahead of the
   weak/advancing upper trough.  With resultant weak lapse rates aloft,
   CAPE should remain limited, tempering storm intensity.  Additional,
   modest shear likewise suggests largely sub-severe storms.  However,
   a locally stronger gust or two cannot be ruled out, and thus will
   maintain 5% wind/MRGL risk across this area.

   ..Goss/Lyons.. 08/07/2021

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z