SPC Day 1 Outlook

   SPC AC 080551

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1251 AM CDT Sun Aug 08 2021

   Valid 081200Z - 091200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE MISSOURI
   VICINITY NORTH-NORTHEASTWARD INTO WISCONSIN...

   ...SUMMARY...
   Scattered strong to severe thunderstorms are possible Sunday from
   Wisconsin and Iowa southward into the Ozark Plateau.  Isolated
   severe storms are also possible across portions of Montana.

   ...Synopsis...
   A mid-level short-wave trough is forecast to make continued eastward
   progress across the central U.S., as a stronger trough/low advances
   across the northwestern states and into the northern Intermountain
   region.  In the East, a weak trough will shift across the
   Mid-Atlantic region through the period.

   At the surface, a strong cold front will move across the Northwest
   and northern Intermountain region, in conjunction with the advancing
   upper system.  A much weaker/rather diffuse surface pattern will
   reside over the central U.S., with convective boundaries likely
   proving more pronounced than any synoptic-scale features.  Weak high
   pressure will largely prevail over the East.

   ...Missouri vicinity to Wisconsin...
   Lingering convection is expected to be ongoing at the start of the
   period, across parts of the upper Mississippi Valley/Upper Great
   Lakes, with diminishing convection/remnant outflows crossing the mid
   Missouri Valley and Kansas/Oklahoma.

   The ongoing convection, and asssociated convective debris/outflows
   cast some uncertainty with respect to environmental evolution
   through the day, but in general, moderate destabilization is
   expected -- aided by a moist boundary layer.  

   By early afternoon, increasing storm development is expected, within
   a zone from eastern Kansas/western Missouri north-northeastward into
   Wisconsin.  Given moderate deep-layer flow, local organization of
   convection will likely result in a few severe storms capable of
   producing mainly damaging winds, along with some hail.  Some upscale
   growth into a band of storms may occur -- with current indications
   suggesting a zone from northern Missouri/southeastern Iowa into
   western Illinois being a more likely location for a more organized
   convective band by late afternoon.

   While convection -- and some severe risk -- will likely continue
   into the evening, a gradual decrease in convective intensity is
   expected diurnally.

   ...Montana...
   A cold front is progged to move across MT today, in conjunction with
   a progressive upper short-wave trough.  Ascent focused along the
   front will support development of a band of convection, though weak
   instability will limit overall convective intensity.  Still, a few
   stronger wind gusts may occur, and thus will maintain MRGL/5% wind
   risk across the region.  Given the weak CAPE, the risk should be
   primarily diurnal, diminishing after sunset with the onset of
   low-level stabilization.

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

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