SPC AC 250558

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1258 AM CDT Tue Apr 25 2017

   Valid 261200Z - 271200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER A PORTION
   OF THE LOWER TO MIDDLE MISSISSIPPI VALLEY REGION...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM A PORTION OF
   THE SOUTHERN PLAINS INTO A PORTION OF THE MIDWEST...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM A PORTION
   OF THE SOUTHERN PLAINS INTO THE GREAT LAKES...

   ...SUMMARY...
   Severe thunderstorms with large hail, damaging wind and possibly a
   few tornadoes are expected across parts of the Arklatex and lower to
   mid Mississippi Valley Wednesday. Isolated severe thunderstorms will
   be possible from Illinois into the southwestern Great Lakes region.

   ...Synopsis...

   Model consensus is that an upper trough will amplify over the
   southern Plains early Wednesday, becoming negatively tilted and
   continuing through the Mississippi Valley Wednesday evening and
   overnight. A lower-amplitude shortwave trough will precede this
   feature and should be located over the upper MS valley at the
   beginning of this period.

   By 12Z Wednesday a cold front should extend from a surface low over
   the upper MS Valley southwestward through northwest TX with a
   dryline farther south through central and southern TX. The cold
   front will continue east and southeast during the day, reaching the
   Great Lakes through TN Valley region Wednesday night.

   ...Southern Plains and lower to middle Mississippi Valley...

   Strengthening low-level jet induced by the approaching shortwave
   trough will advect mid to upper 60s F boundary-layer dewpoints
   through the pre-frontal warm sector beneath 7-7.5 C/km mid-level
   lapse rates. These processes will contribute to moderate instability
   with 1500-2500 J/kg MLCAPE, despite the potential for widespread low
   clouds which will limit diabatic warming in some areas.
   Thunderstorms will likely be in progress within baroclinic zone and
   along warm conveyor belt from portions of OK into MO, and some of
   this activity could pose an ongoing modest risk for a few strong
   wind gusts and hail. However, primary development of severe storms
   is expected during the afternoon as storms intensify along and just
   ahead of the cold front and in association with a destabilizing warm
   sector. Strong dynamic forcing for ascent within frontal zone
   augmented by the negatively tilted shortwave trough and
   strengthening low-level jet will likely result in the initiation of
   numerous storms and an eventual upscale linear growth. Strong
   deep-layer winds, vertical shear and large low-level hodographs will
   favor organized storms including embedded supercells and bowing
   segments, with all severe hazards possible.  

   ...Illinois into the Great Lakes...

   Instability and low-level moisture will be less in this region
   compared to farther south but sufficient for an organized severe
   threat given favorable wind profiles. The stronger storms will
   likely expand into this region during the late afternoon and
   evening, with a few supercells and bowing linear segments capable of
   damaging wind, large hail and a couple of tornadoes.

   ..Dial.. 04/25/2017

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