SPC AC 200726

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0226 AM CDT Sat Jun 20 2020

   Valid 221200Z - 231200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTHERN AND CENTRAL PLAINS INTO THE LOWER MISSOURI AND UPPER
   MISSISSIPPI VALLEYS...

   ...SUMMARY...
   Strong to severe thunderstorms will be possible Monday afternoon and
   evening from the eastern Texas Panhandle northeastward into the
   Upper Mississippi Valley. Wind damage and isolated large hail will
   be the primary threats.

   ...Southern and Central Plains/Lower Missouri Valley/Upper
   Mississippi Valley...
   An upper-level trough will move eastward across the central and
   northern Plains on Monday. At the surface, a cold front is forecast
   to advance southeastward across the central Plains and mid Missouri
   Valley. Ahead of the front, a very moist airmass will be in place
   with surface dewpoints from the mid 60s to lower 70s F. In response
   to surface heating, moderate to strong instability should develop by
   afternoon across much of the warm sector. Model forecasts suggest
   that convective initiation will take place along parts of the front
   during the late afternoon with the greatest coverage from Kansas
   into Missouri and Iowa. NAM and GFS forecast soundings along this
   part of the front generally have 0-6 km shear in the 40 to 50 kt
   range. This wind profile will be favorable for a severe threat with
   supercells and the better organized line segments. Further to the
   east across the warm sector, pre-existing outflow boundaries could
   also be a focus for convective development. The current thinking is
   that a mixed mode will be most possible but there is still
   uncertainty. If a cluster of discrete cells can persist, then large
   hail and wind damage would be the primary threats. If a quick
   transition to linear mode occurs, then wind damage could be the
   primary threat.

   Further to the southwest into southern Kansas, northern Oklahoma and
   the Texas Panhandle, large-scale ascent should be considerably less
   further away from the central U.S. upper-level trough. In spite of
   this, convection should form along the front as low-level
   convergence increases during the late afternoon. Forecast soundings
   from the eastern Texas Panhandle northeastward into northern
   Oklahoma by early evening show MLCAPE in the 3000 to 4000 J/kg range
   and have 0-6 km shear of 35 to 45 kt. This will be favorable for
   severe storms with cells that can develop in the warm air aloft. The
   more intense cores with access to the strongest instability should
   have a threat for isolated large hail. Wind damage will also be
   possible especially if a line segment can form along the front.

   ..Broyles.. 06/20/2020

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