SPC AC 040553

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1253 AM CDT Thu Jul 04 2024

   Valid 041200Z - 051200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
   MISSISSIPPI VALLEY AND FROM THE MISSOURI OZARKS INTO THE SOUTHERN
   PLAINS...

   ...SUMMARY...
   Severe thunderstorms will be possible across parts of the Upper
   Mississippi Valley, Ozarks, and southern Plains.

   ...Discussion...

   Seasonally strong upper trough is shifting east across the northern
   Plains early this morning. This feature is forecast to advance
   toward the middle MO Valley by late afternoon as 500mb, 60kt speed
   max translates across southeast NE into IA. Left exit region of this
   speed max will spread across the upper MS Valley along with a
   corridor of modest 12hr mid-level height falls. Latest model
   guidance suggests a weak surface low will develop and track along
   the MN/IA border into southwest WI by late evening. This corridor
   appears favorable for robust convective development as boundary
   layer warms and convective temperatures are breached, likely by
   midday, as readings warm through the upper 70s-80F. Forecast
   soundings exhibit veering wind profiles with height, and some
   supercell potential exists within this zone of focused ascent. Large
   hail and locally damaging winds are the primary concerns.

   Farther south, an expansive corridor of convection has evolved over
   the central Plains early this morning. Upscale growth may continue
   for the next few hours, and a long-lived MCS should propagate across
   eastern KS into MO by sunrise. While this complex may not be
   particularly severe at daybreak, a long-lived MCS, or its remnants,
   will advance downstream into the OH Valley as modest mid-level flow
   will extend along a corridor from MO into southern OH. Models are
   not too aggressive in steepening low-level lapse rates east of the
   MS River later today, but some surface heating is expected to
   contribute to increased buoyancy that will likely contribute to new
   robust updrafts developing along the MCS outflow/differential-
   heating zone. Will maintain MRGL risk across this region, although
   somewhat higher severe probabilities may be warranted, especially
   across KY along the southern flank of the forward-propagating MCS.

   Later in the day, very strong surface heating across the southern
   Plains will result in steep surface-3km lapse rates from northwest
   TX, across central into northeast OK. As the northern Plains trough
   shifts east, mid-level flow will begin to turn more westerly across
   northern OK, and 500mb speeds will increase to 25-40kt north of
   I-40. Convective temperatures will be breached by 22z, just ahead of
   the surface front, and scattered thunderstorms should easily develop
   along the wind shift. PWs will be very high across this region with
   values in excess of 2 inches. With temp/dew point spreads around
   30F, there is increasing confidence that the most robust convection
   should generate severe downdrafts. A fairly concentrated corridor of
   convection should evolve downstream into the MO Ozarks by early
   evening.

   ..Darrow/Squitieri.. 07/04/2024

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