SPC May 21, 2025 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0718 AM CDT Wed May 21 2025

Valid 211300Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS IN THE OZARKS TO
MID-SOUTH AND FAR EASTERN NC...

...SUMMARY...
The most likely corridors for severe storms are across parts of far
eastern North Carolina this afternoon, and the Ozarks into the
Mid-South this evening.

...Eastern NC and southern VA...
Morning surface analysis places a low over the Piedmont with a
reservoir of lower 70s dewpoints over the coastal plain of eastern
NC to the south of a residual frontal zone.  A mid-level vorticity
maximum rotating through the base of an Upper Midwest larger-scale
trough, will move from the IL/IN vicinity to the Mid-Atlantic states
by early evening.  A weakened surface cold front will push east
across the Carolinas during the day as the aforementioned low
develops east of the Outer Banks by early evening.  Diurnal heating
today will support 1500-2500 J/kg MLCAPE. A couple of supercells may
develop ahead of the cyclone, most likely across far eastern NC and
the Outer Banks. A tornado or two, isolated large hail, and
localized severe gusts are the expected hazards.

...Ozarks/Mid-South...
While rich boundary-layer moisture will remain confined across south
TX/LA, a strengthening low-level baroclinic zone is expected during
the afternoon to evening near the KS/OK border east-southeast into
the Mid-South. Guidance is rather consistent in developing at least
elevated convection to the cool side of this zone by evening. This
will be coincident with an intensifying mid-level speed max.
Forecast soundings depict potentially very strong mid to upper-level
speed shear within the slightly north of west flow regime. Coupled
with steep mid-level lapse rates, this setup could yield a few
elevated supercells capable of large hail and perhaps wind. 

...Central Plains...
A mid-level vorticity lobe initially over WY this morning will move
east-southeast into the lower MO Valley by early evening within a
west-northwest flow regime.  Heating will result in very steep 0-3
km lapse rates by mid afternoon with several hundred J/kg SBCAPE. 
Elongated hodographs will support quick-moving cells capable of an
isolated risk for severe gusts during the 20-01z period.  

...Upper OH Valley...
A confined corridor of modest boundary-layer heating may occur
downstream of the primary surface cyclone drifting across northern
OH to Lake Erie. Coupled with cooling mid-level temperatures, weak
surface-based buoyancy is expected by midday into the afternoon.
Deep-layer shear will not be strong given proximity to the mid-level
trough, but should be adequate for weak/transient mid-level
rotation. With numerous thunderstorms expected, small to marginally
severe hail and isolated damaging winds are anticipated. A brief
tornado is also possible with storms crossing the warm front before
convection weakens abruptly eastward.

...North FL and south GA...
Along the southeastward-moving cold front, moderate buoyancy is
expected ahead of the front.  A veered low-level wind profile will
limit effective bulk shear, but scattered thunderstorms could yield
multicells and perhaps a transient supercell.  Isolated damaging
winds and marginally severe hail are possible with the stronger
storms.

...Deep South TX...
Not much change from previous forecast thinking in that a very
unstable airmass will evolve by mid-late afternoon. While
large-scale signals for ascent are nebulous, convection will likely
develop in northeast Mexico over the higher terrain this afternoon.
Some of this activity may spread east across the lower Rio Grande
Valley this evening.  Weak winds through the lower half of the
buoyancy profile will be a limiting factor, but isolated severe
hail/wind may accompany any isolated and mature storm.

..Smith/Marsh.. 05/21/2025

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