Severe Storm Outlook Narrative (AC)
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ACUS02 KWNS 210602
SPC AC 210600

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Tue May 21 2024

Valid 221200Z - 231200Z


Severe thunderstorms posing a risk for damaging gusts and hail will
be possible from central Texas into the Ohio Valley and lower Great
Lakes vicinity on Wednesday. The highest concentration of damaging
gusts and large to very large hail is expected from north Texas to
the Missouri Bootheel vicinity.


An upper shortwave trough will move northeast across the Upper
Midwest/Great Lakes vicinity on Wednesday. Meanwhile, convectively
enhanced vorticity maxima from the Day 1/Tue period will develop
east/northeast across parts of the Ohio Valley/Lower Great Lakes
area in broad southwesterly deep-layer flow. Further south, broad,
enhanced southwesterly flow will persist over the southern Plains to
the Mid-South. One or more shortwave impulses are expected to float
through this area ahead of a deepening large-scale western U.S.
upper trough.

At the surface, an occluding low near the MN/Ontario border will
lift north through the period, with a weak surface trough extending
into parts of the upper Ohio Valley and lower Great Lakes. The
northern extent of a surface cold front will progress eastward
across the Great Lakes vicinity. Meanwhile, the front will mainly
stall from IN/southern IL into central OK and northwest TX. A
dryline will move east into central TX. These boundaries will become
the focus for thunderstorm development during the afternoon.

...Texas to Southern IL...

A moisture-rich boundary layer will be present, with dewpoints in
the upper 60s to low 70s F common. Atop this moist boundary layer,
steep midlevel lapse rates around 8 C/km are forecast. This will
result in strong to extreme instability (2500-4000 J/kg MLCAPE).
Vertical shear will be favorable for supercells, with modestly
enlarged low-level hodographs become elongated/straight above 3 km.
Significant hail (greater than 2 inch diameter) will be possible
with initial supercell development. How long semi-discrete
supercells will be maintained is a bit uncertain. Upscale
development into bowing segments will likely occur, resulting in an
increasing damaging wind risk with time. A 35-45 kt southwesterly
low-level jet is forecast to increase by early evening. This will
support increasing 0-1 km SRH (to around 200 m2/s2) and a few
tornadoes will be possible. A strong tornado cannot be ruled out,
especially over parts of AR into north Texas.

...IN/KY to the Lower Great Lakes...

Forcing for ascent across the region will mainly be provided by any
MCVs from remnant Day 1/Tue convection floating through
southwesterly flow, and the eastward-advancing cold front. A moist
airmass with dewpoints in mid/upper 60s will be present over
IN/OH/KY, with low/mid 60s extending northeast into NY/PA and
vicinity. Strong heating and a plume of steep midlevel lapse rates
will support moderate destabilization during the late
morning/afternoon. Vertical shear will be sufficient for organized
cells, though decreasing with northeast extent into eastern NY and
the Mid-Atlantic vicinity. Isolated damaging gusts and marginal hail
will be possible with thunderstorms into early evening.

..Leitman.. 05/21/2024