SPC 2000Z Day 1 Outlook

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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0240 PM CDT Mon May 03 2021

Valid 032000Z - 041200Z



The greatest severe-thunderstorm threat appears to be from late
afternoon through tonight in a corridor from northeast Texas and
southeast Oklahoma to the Lower Ohio Valley. Very large hail,
tornadoes (a couple of which may be significant), and intense
damaging winds are expected.

...20z Update...

Only minor adjustments have been made to the convective outlook with
the 20z update. The main change is to trim the Marginal and Slight
risk areas across parts of IA/MO based on the current location of
the surface cold front and ongoing/developing convection. Other
minor adjustments have been made to the Slight risk area across
parts of upstate SC into central NC based on current observations
and radar trends. Otherwise, the forecast philosophy remains
unchanged from the previous outlook. See below for the previous
discussion, and reference MCDs 494, 495, 496, and 497 for near-term

..Leitman.. 05/03/2021

.PREV DISCUSSION... /ISSUED 1123 AM CDT Mon May 03 2021/

...Southern Great Plains to Mid-South...
Two primary corridors of severe thunderstorms are expected to
develop by late afternoon. The first within a post-frontal regime
off the higher terrain of NM spreading east across the TX South
Plains towards the Big Country and western north TX. Very steep
mid-level lapse rates in conjunction with robust speed shear in the
mid-upper portion of the thermodynamic profile should prove
favorable for a long-track supercell or two with a primary hazard of
large to significant severe hail. 

The second area of severe thunderstorms will rapidly develop along
the dryline to surface front intersection across central TX before
spreading into southeast OK. Large buoyancy given the very steep
mid-level lapse rates will support intense supercells capable of all
hazards, some of which will be significant. Guidance still differs
on the degree of low-level flow response this evening rendering
uncertainty over how long discrete supercells will be maintained.
Given rich boundary-layer moisture coupled with the large MLCAPE,
there is concern for at least conditional significant tornado
potential across a portion of north TX into southeast OK. If upscale
growth occurs too quickly, this may not be realized, but have
highlighted a corridor of enhanced tornado potential in this region.
Otherwise, upscale growth will occur at some point this evening
rendering a predominant severe wind threat spreading east-northeast
towards the Mid-South through tonight.

Scattered thunderstorms will persist across a broad swath of the
southeast states through this evening. A shortwave trough over the
OH Valley will move east with the belt of stronger low/mid-level
flow to its southeast focused across the Carolinas and VA. Along the
periphery of moderate buoyancy, the threat for a few tornadoes and
scattered damaging winds should develop from GA to southeast VA. 

Farther west, low-level flow will become increasingly veered and
slowly subside through the afternoon. However, larger buoyancy along
the eastern periphery of the EML emanating east from the
south-central states will maintain a threat for scattered damaging
winds and large hail.

An MCV over northeast MO will be the primary mechanism for scattered
thunderstorm development across the Mid-MS Valley into IL late
today. Abundant cloud coverage downstream should delay the severe
storm threat until at least late afternoon. An additional swath of
severe storm development is anticipated along the cold front in MO
where more robust boundary-layer heating is underway. This activity
will likely grow upscale into an east-southeast moving MCS towards
the Lower OH Valley region this evening with damaging winds becoming
the primary hazard.

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