SPC AC 211730

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1230 PM CDT Sat Jul 21 2018

   Valid 221200Z - 231200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SUNDAY AFTERNOON
   AND EVENING FROM THE FL PANHANDLE INTO SOUTHEAST GA AND OVER PARTS
   OF THE NORTHERN PLAINS...

   ...SUMMARY...
   A few severe thunderstorms are possible Sunday afternoon and evening
   across parts of the FL Panhandle and southern GA, and across parts
   of the northern Plains.

   ...Synopsis...
   Overall upper pattern across the CONUS, characterized by ridging
   center over the southern Rockies and troughing center over the
   middle OH valley, is expected to change little throughout the period
   Sunday. Enhanced northwesterly flow aloft will extend southeastward
   from the MO Valley to the central Gulf Coast between these two
   primary features. Farther north, a more progressive shortwave trough
   will move from southern Saskatchewan eastward/northeastward into
   central Manitoba while moderate westerly flow aloft extents through
   its southern periphery from the northern Rockies through the
   northern Plains. 

   At the surface, an occluded low will slowly drift southward from the
   middle OH Valley into the TN Valley while another low pivots
   northwestward across the Lower Great Lakes. A weak frontal zone is
   expected along the base of the upper ridge, extending roughly from a
   lee low over the Carolina Piedmont southwestward to southern AL/MS
   and then back northwestward to a lee low over the central High
   Plains. Farther north, a cold front attendant to the
   Saskatchewan/Manitoba shortwave trough will move through the
   northern and central Plains Sunday afternoon and evening.

   ...Northern/Central Plains...
   Expectation is for the previously mentioned cold front to extend
   from central ND southward through the NE Panhandle at 18Z with
   gradual eastward progress anticipated thereafter. By 12Z Monday, the
   cold front will likely extend from north-central MN southwestward
   into southwest NE. Modest moisture return is anticipated across the
   northern Plains ahead of the approaching cold front, which when
   combined with strong insolation, will result in airmass
   destabilization. The strongest forcing for ascent will occur across
   southern Saskatchewan/Manitoba and adjacent portions of ND.
   Consequently, the highest likelihood for thunderstorms exists here.
   Modest instability coupled with seasonally strong westerly flow
   aloft is expected to support a few strong to severe storms in this
   area. Gradually decreasing thunderstorm coverage is expected
   southward through SD, largely due to further displacement from the
   stronger forcing for ascent. A secondary increase in thunderstorm
   coverage is possible across northeast CO as storms come off the
   higher terrain. Decreasing shear with southern extent is expected to
   keep the severe threat more isolated that areas farther north.

   ...Central Gulf Coast...FL Panhandle/Northern
   FL...Southern/Southeast GA...
   Some potential exist for storms to be ongoing across the region at
   the beginning of the period but an overall scouring of the airmass
   is not currently anticipated. As such, strong instability is
   expected to develop from the central Gulf Coast eastward to the
   southeast GA coast amidst favorable low-level moisture (i.e.
   dewpoints in the mid 70s), seasonally cool mid-level temperatures,
   and strong daytime heating. Enhanced northerly/northwesterly flow
   aloft is also anticipated across the region, leading to a higher
   chance of storm organization than typically experienced this time of
   year. Primary severe threat will be damaging wind gusts.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:   2%     - Marginal
   Wind:     15%     - Slight
   Hail:     15%     - Slight

   ..Mosier.. 07/21/2018

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