SPC AC 041936

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0236 PM CDT Thu Jul 04 2024

   Valid 042000Z - 051200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
   MISSISSIPPI VALLEY...AND FROM THE SOUTHERN PLAINS TO THE OHIO
   VALLEY...

   ...SUMMARY...
   Scattered severe thunderstorms will be possible through this evening
   across parts of the upper Mississippi Valley, and from the southern
   Plains to the lower Ohio Valley.

   ...20z Update...

   Severe probabilities have been trimmed across parts of MN/IA in-line
   with the current location of the surface cold front. Otherwise, only
   minor changes have been made to the 10 percent general thunderstorm
   line. Overall forecast thinking remains similar to the previous
   outlook. However, coverage of severe storms across parts of southern
   IL into the Ohio Valley (outside of WW 505) is uncertain the
   remainder of the period. However, a very moist and unstable airmass
   resides across the area. Additional storms may develop this
   evening/overnight along the surface front, and any other storms that
   can develop through evening would pose severe gust potential,
   precluding a downgrade in probabilities at this time. 

   For information on short term severe potential across the Upper MS
   Valley and the southern Plains, reference MCDS 1534 and 1535.

   ..Leitman.. 07/04/2024

   .PREV DISCUSSION... /ISSUED 1130 AM CDT Thu Jul 04 2024/

   ...Synopsis...
   An upper trough over the northern/central Plains will move generally
   eastward today across the Upper Midwest and mid MS Valley. A
   separate, convectively augmented mid-level vorticity maximum is
   present over southern IA/northern MO late this morning. This MCV and
   associated convection across the OH Valley will move
   east-northeastward across the OH Valley/Midwest through this
   evening. At the surface, a weak low should develop eastward across
   parts of the Upper Midwest in tandem with the large-scale upper
   trough. Another weak surface low should also track northeastward
   over the OH Valley with the remnant MCV. A convectively reinforced
   front draped from the southern Plains northeastward into the mid MS
   and OH Valleys will likely serve as a focus for strong to severe
   thunderstorms this afternoon and evening.

   ...Mid Mississippi Valley into the Ohio Valley and Mid-Atlantic...
   Mostly elevated thunderstorms are ongoing late this morning across
   the lower OH Valley. The rather moist low-level airmass along/south
   of a front will continue to gradually destabilize through the
   afternoon. Although mid-level lapse rates will remain poor, moderate
   instability has already developed downstream of activity moving
   across southern IN and western KY. Additional intensification of
   this convection will probably occur through early afternoon across
   parts of central/eastern KY and perhaps southern OH ahead of the
   MCV. Even though stronger mid-level flow may tend to remain
   displaced to the north of the front, modest but sufficient
   deep-layer shear should be present to support multicell clustering.
   Scattered damaging winds occasionally reaching severe thresholds
   should be the main threat with this activity as it spreads eastward
   across the lower OH Valley this afternoon and evening. Low-level
   flow is forecast to remain generally modest and veered to
   southwesterly. Still, sufficient speed shear will be present to
   support some threat for updraft rotation and perhaps a tornado or
   two, especially if any supercells can develop and persist. Isolated
   hail may also occur with more robust cores. Confidence in strong
   convection moving off the Blue Ridge Mountains in the Mid-Atlantic
   is relatively low. But, any thunderstorms that do form across this
   region could produce locally damaging winds.

   ...Southern Plains to the Ozarks...
   The portion of the cold front extending across the southern Plains
   into the Ozarks is forecast to make only slow southward progress
   through this evening. Even with some mid/high-level clouds
   persisting across these areas, robust daytime heating along/south of
   the front will likely encourage surface temperatures to warm into
   the 90s and low 100s. Even though low/mid-level flow will remain
   fairly weak, rather large surface temperature/dewpoint spreads (up
   to 30-40 degrees F) and steepened low-level lapse rates should
   foster a threat for mainly severe/damaging winds with any
   thunderstorms that can develop this afternoon and evening. Robust
   convection appears probable along/near the front by 22-00Z, and
   there appears to be some potential for an organized cluster to
   develop over the Ozarks/southern MO vicinity and sweep
   east-southeastward through the late evening.

   ...Upper Mississippi Valley...
   A focused area of ascent associated with the upper trough will
   overspread southern MN and northern IA today. While cloud cover
   remains prevalent over much of this region late this morning, there
   has been some recent clearing on the western edge of the cloud deck.
   A relatively small area of modest destabilization is still
   anticipated, with MLCAPE around 1000-1500 J/kg possible. A 45-60 kt
   mid-level jet attendant to the upper trough will overspread the
   developing warm sector through the afternoon. This jet will aid
   sufficiently strong deep-layer shear to support supercells with an
   associated threat for severe hail. Some clustering/upscale growth
   may eventually occur, which would support a greater threat for
   severe/damaging winds. This activity should weaken by late evening
   into WI and northern IL as it encounters a less unstable airmass.

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