SPC AC 081751

   Day 2 Convective Outlook CORR 1
   NWS Storm Prediction Center Norman OK
   1251 PM CDT Thu Apr 08 2021

   Valid 091200Z - 101200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FRIDAY THROUGH
   FRIDAY NIGHT ACROSS PARTS OF SOUTHEASTERN OKLAHOMA...NORTHEASTERN
   TEXAS...SOUTHERN ARKANSAS...NORTHERN LOUISIANA...CENTRAL AND
   SOUTHERN MISSISSIPPI AND ADJACENT PORTIONS OF WESTERN ALABAMA...

   CORRECTED FOR TYPOS/WORDING

   ...SUMMARY...
   Severe thunderstorms are possible across parts of the southeastern
   Great Plains into the lower Mississippi Valley and central Gulf
   Coast States Friday through Friday night.  This may include the
   development of one or two organized thunderstorm clusters, with the
   potential to produce swaths of damaging wind gusts.  Large, damaging
   hail and a couple of tornadoes are also possible.

   ...Synopsis...
   A deep mid-level low is already in the process of migrating
   northeast of the lower Missouri Valley.  This should continue
   through Friday and Friday night, as blocking remains prominent
   within the downstream flow, and another vigorous upstream short wave
   (emerging from the northern mid-latitude Pacific) continues inland,
   across the Rockies into the Plains.

   The lead impulse and associated surface cyclone are forecast to
   continue to weaken, while migrating across and northeast of the
   Upper Midwest and Great Lakes region by late Friday night.  The cold
   front trailing the cyclone currently curves from the Upper Midwest
   through the lower Ohio and Mississippi Valleys, and is already
   becoming increasingly diffuse.  As this continues, models suggest
   considerable boundary-layer moistening will occur into and through
   this period across a broad area of the southeastern Great Plains and
   lower Mississippi Valley.  It appears that this will coincide with
   the northeastward advection of elevated mixed-layer air, on the
   southwestern periphery of the departing mid-level troughing, and
   ahead of a perturbation emerging from the southern mid-latitude or
   subtropical eastern Pacific.

   Models indicate that this southern perturbation  will accelerate
   across Texas into the lower Mississippi Valley by late Friday night,
   within west-northwesterly to westerly flow in advance of the digging
   short wave of northern mid-latitude Pacific origin.  It appears that
   associated forcing for ascent will contribute to new surface
   cyclogenesis across the southern Great Plains into the lower
   Mississippi Valley/Mid South vicinity by 12Z Saturday.

   ...Southeastern Great Plains into central Gulf States...
   While there appears reasonable model consensus on the general
   large-scale pattern evolution, considerable spread does exist
   concerning the synoptic and, particularly, the sub-synoptic
   developments for this period.  Given moistening low-levels in the
   presence of steepening mid-level lapse rates, it does appear that
   substantial mixed-layer CAPE could develop Friday, in the  presence
   of strong vertical shear.  This provides support for the risk of
   severe storm development, though the extent and focus/details remain
   unclear at the present time.  Based on the latest guidance, there
   does appear potential for the evolution of multiple clusters of
   severe storms Friday and Friday night, with isolated to widely
   scattered discrete supercell development also possible.

   There does appear a consistent signal in the model output that
   large-scale ascent along a strengthening mid-level baroclinic zone
   may provide support for increasing thunderstorm development across
   the Ark-La-Tex vicinity through southern Arkansas by mid day Friday.
    As the boundary-layer destabilizes, there appears potential for
   this activity to evolve into an intensifying and organizing
   mesoscale convective system, which will tend to advect/propagate
   eastward across the north central Mississippi/Alabama vicinity
   before weakening Friday evening.

   The approach of the southern mid-latitude/subtropical Pacific
   impulse may contribute to renewed thunderstorm development upstream,
   along the trailing convective outflow, by Friday evening.  This may
   evolve into another organizing cluster of severe storms, which will
   probably tend to develop east-southeastward across the lower
   Mississippi Valley through early Saturday.

   Given the steep mid-level lapse rates, sizable CAPE and strong
   shear, stronger initial storm development may be accompanied by the
   risk for large, damaging hail, before activity grows upscale with
   damaging wind gusts becoming the more prominent hazard, along with
   the possibility of a few tornadoes.

   ..Kerr.. 04/08/2021

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