SPC 1730Z Day 2 Outlook

Day 2 Outlook Image

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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