NWS Storm Prediction Center - Day 2 Convective Outlook

Apr 22, 2021 1730 UTC Day 2 Convective Outlook
Updated: Thu Apr 22 17:30:23 UTC 2021
SPC Day 2 1730Z Outlook Categorical SPC Day 2 1730Z Outlook Categorical Legend

 Forecast Discussion - Day 2 Convective Outlook

   SPC AC 221730

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1230 PM CDT Thu Apr 22 2021

   Valid 231200Z - 241200Z


   Isolated to scattered severe thunderstorms are expected Friday into
   Friday night from parts of the southern Plains into the lower
   Mississippi Valley/central Gulf Coast states. Large to very large
   hail, damaging winds, and isolated tornadoes all appear possible.

   As broad cyclonic flow around a Canadian Maritimes upper low
   gradually departs from the Northeast, the primary feature of
   interest will be a short-wave trough moving out of the Intermountain
   West into/across the Plains states.  With time, the southern portion
   of this trough -- advancing more quickly than farther north -- will
   cross the Ozarks/Arklatex and then the lower Mississippi Valley
   overnight, resulting in a gradually more negative tilt to the
   larger-scale trough.

   At the surface, a low is progged to reside over the southern High
   Plains/in lee of the southern Rockies.  As the upper trough
   advances, surface low pressure will shift eastward in a loosely
   defined manner, while a dryline mixes eastward into central Texas
   during the day and a warm frontal zone extends eastward into the
   central Gulf Coast states.  By the end of the period, a cool front
   will be sweeping across Texas in the wake of the primary surface low
   expected to reside in the vicinity of the Arklatex by 24/12z.

   ...Southern Plains to the central Gulf Coast states...
   A somewhat complex convective scenario is apparent Friday, as upper
   troughing moves into/across the south-central U.S., along with an
   associated weak/rather ill-defined surface pattern.  

   As the upper trough advances, and a surface high shifts eastward
   into the western Atlantic, increasing southerly low-level flow into
   the south-central states will advect Gulf moisture northward beneath
   steep lapse rates aloft overspreading the southern Plains through
   the day.  As a dryline mixes quickly eastward into central Texas
   during the first half of the period, large-scale ascent and an
   increasingly favorable thermodynamic environment should support
   central Texas storm development.  Strong/veering winds with height
   across the area suggests that storms will quickly acquire rotation.
   While CAMs may be a bit early and aggressive initially, with respect
   to storm coverage, isolated supercells -- accompanied by a risk for
   very large hail during the afternoon -- will likely congeal into a
   cluster of more numerous storms, moving eastward across northeastern
   Texas/the Arklatex region by late afternoon/early evening.  

   Meanwhile, a second area of convective development is expected
   farther north, from northwest Texas and eastern portions of the
   Texas Panhandle area east-northeastward across northern Oklahoma and
   southeastern Kansas into Missouri, near a secondary low and its
   associated/weak warm front.  A drier boundary layer across this area
   -- and thus correspondingly lesser CAPE -- should limit severe risk
   a bit.  However, large hail -- particularly over the northwestern
   Texas and Oklahoma portions of the area -- remains apparent.

   By evening, as convection congeals across the Arklatex area, risk
   for damaging winds will likely become a bit more widespread.  CAMs
   suggest that this storm cluster -- aided by very favorable shear --
   could organize into at least a loosely organized bowing MCS during
   the evening, which would shift eastward across the lower Mississippi
   Valley and later the central Gulf Coast states overnight, along a
   warm frontal zone.  While somewhat limited low-level moisture -- and
   thus possibly a very weakly stable boundary layer -- is expected,
   risk for at least locally damaging winds is apparent, particularly
   if convection organizes in an upscale manner as anticipated. 
   Additionally, an intensifying southerly low-level jet implying
   strong warm advection may support a gradual increase in cellular --
   and likely rotating -- convection ahead of the main cluster of
   storms.  Given the presence of the warm front, and increasingly
   favorable veering/increasing of the low-level flow field with
   height, risk for a couple of tornadoes also remains apparent, given
   what should be a not-prohibitively-stable boundary layer in the
   vicinity of, and to the south of, the warm front.

   While CAMs suggest that a fairly well-organized bowing convective
   line may be shifting across Alabama late in the period, a slightly
   more stable boundary layer may preclude more widespread wind risk,
   and thus an eastward expansion of the SLGT risk area will not be
   initiated at this time.

   ..Goss.. 04/22/2021



Data courtesy the Storm Prediction Center
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