SPC AC 051953

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0253 PM CDT Tue Sep 05 2023

   Valid 052000Z - 061200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE UPPER MISSISSIPPI VALLEY/WESTERN UPPER GREAT LAKES REGION...AND
   FROM MISSOURI AND VICINITY SOUTHWESTWARD INTO NORTHEASTERN
   OKLAHOMA...

   ...SUMMARY...
   Severe thunderstorms are expected this afternoon and evening over
   parts of the upper Mississippi Valley/Lake Superior region, and
   across the Ozarks and parts of Oklahoma. Severe wind gusts and
   isolated large hail are possible.

   ...Discussion...
   Along with minor line tweaks in a few areas, including some eastward
   expansion of thunder into parts of Wyoming for the overnight period,
   the only other substantive change at this time is the northward
   expansion of SLGT risk/15% wind into parts of northern Missouri. 
   Here, a similar thermodynamic pre-frontal environment is indicated
   as compared to areas a bit farther south, and several CAM runs are
   indicating development along the front may extend a bit farther
   north than previously hinted at in the outlook.

   Otherwise, expectations remain similar to those in prior outlooks.

   ..Goss.. 09/05/2023

   .PREV DISCUSSION... /ISSUED 1131 AM CDT Tue Sep 05 2023/

   ...Upper Mississippi Valley...
   A shortwave trough over the Dakotas this morning will continue
   eastward toward the upper Mississippi Valley through tonight. A
   slight cooling of mid-level temperatures (-10C at 500 mb) will
   accompany this trough, while only a modest strengthening of
   trough-preceding winds aloft is expected, given that the trough is
   somewhat removed from the stronger westerlies over the Canadian
   prairies.

   While some warm-sector cloud cover persists early today regionally,
   the boundary layer ahead of an eastward-moving cold front should
   become minimally inhibited by early into mid-afternoon, with MLCAPE
   reaching 2500+ J/kg especially across the eastern halves of
   Minnesota and Iowa, as well as much of western Wisconsin and far
   northwest Illinois. Initial thunderstorm intensification is expected
   this afternoon across northern/central Minnesota, potentially with
   an ongoing band of storms across northern Minnesota, and more so
   near the aforementioned front and surface wave, with subsequent
   scattered development southward into southeast Minnesota/eastern
   Iowa and western Wisconsin through late afternoon and early evening.
   Severe wind gusts and hail will be possible with a mixed mode of
   storms including multicells and some transient supercells. Some
   tornado risk may exist as well, mainly across northeast
   Minnesota/northwest Wisconsin. 

   ...Middle Mississippi Valley/Ozarks/southern Plains... 
   Widely scattered mid-level convection across the region trails a
   shortwave trough centered generally near the confluence of the
   Mississippi/Ohio Rivers. This convection is atop a warm-sector
   boundary layer that will heat and become strongly unstable by peak
   heating, particularly across eastern Oklahoma into Missouri
   western/northern Arkansas ahead of an east/southeastward-moving
   front. 

   Isolated to widely scattered thunderstorms are expected to develop
   by mid/late afternoon near the front, and somewhat across the warm
   sector, potentially influenced by lingering cloud cover/zones of
   differential heating. While tropospheric winds will only be modest
   strength (effective shear less than 30 kt), strong heating, steep
   lapse rates, and ample buoyancy will support the potential for
   severe-caliber wind gusts, especially with the aforementioned
   corridor of greatest destabilization. Some severe hail may occur as
   well.

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