412
ACUS01 KWNS 261258
SWODY1
SPC AC 261256

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0756 AM CDT Sun May 26 2024

Valid 261300Z - 271200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE
EASTERN OZARKS TO PARTS OF THE OHIO VALLEY REGION...

...SUMMARY...
Multiple rounds of severe storms are possible from the Ozarks and
nearby Mississippi Valley into the Ohio Valley States today, with
threats for tornadoes, severe gusts and occasional large hail.

...Synopsis...
A progressive mid/upper-level pattern is apparent across the CONUS,
perturbed mainly by a synoptic-scale trough initially over the
central High Plains, and related cyclonic flow and embedded
vorticity maxima/shortwaves over the Central States.  The trough
should shift eastward to WI, eastern IA, northern MO and central OK
by 00Z, then over the Upper Great Lakes, Lower MI, and the lower
Ohio Valley by 12Z tomorrow.

At the surface, 11Z analysis showed a primary synoptic low over
southwestern IA, with warm front across western IL behind convective
outflow, and ahead of the outflow from central IL across southern IN
to northeastern KY.  The warm front should move slowly northward
across the Ohio Valley through the afternoon.  The cold front was
drawn from the IA low southwestward to another low between ICT-PNC,
then across western OK and northwest TX.  This front will overtake a
dryline today over northwest/west-central TX.  By 00Z, the cold
front should extend from a triple-point low near MSN across central
IL, southern MO, southeastern OK, and north-central/central TX.  By
12Z, the cold front should reach eastern IN, central KY, and western
TN, becoming quasistationary southwestward over the Arklatex to
central TX.  The cold front will be preceded by an MCS outflow
boundary over parts of the Ozarks and Ohio Valley region today.

...Ozarks/Arklatex to Ohio/Tennessee Valleys and south-central
Appalachians...

A complex, multi-episode severe scenario is apparent, still bearing
some important mesoscale uncertainties.  However, probabilities
supporting an "enhanced" category appear solidly warranted over most
of the original area that has not been too convectively processed,
and mesoscale foci may yield denser swaths of severe (wind in
particular) within that remaining broad corridor.

An ongoing severe MCS, with embedded supercells and bowing segments
and a history of several overnight tornadoes in the Ozarks, will
continue to pose a threat for all severe hazards (including
tornadoes) for at least the next several hours past midday.  This
threat should persist as activity exits the Ozarks, crosses the
adjoining Mississippi Valley, and moves into parts of the lower Ohio
Valley vicinity.  Some northward expansion toward/past the warm
front is possible over the Ohio Valley.  This activity should only
gradually outpace the most favorable buoyancy as it approaches the
Appalachians, and may still have a severe threat across the higher
terrain.  Confidence in its persistence is heightened by the
presence of at least one MCV over the eastern Ozarks, which should
enhance ascent and lower/middle-tropospheric vertical wind
profiles/shear on the mesoscale.  Organization of these
thunderstorms should continue to take advantage of forced lift with
cold pools, as well as lift from internal rotational dynamics of
supercells and bookend vortices, to overcome modest MLCINH this
morning through midday.  Inflow air will contain rich low-level
moisture (surface dewpoints commonly in the upper 60s to low 70s F,
locally higher), and will be diurnally destabilizing from heating
and warm advection near and south of the warm front.  For near-term
guidance, see SPC Tornado Watch 314 and related mesoscale
discussions.

Details of subsequent round(s) of convection still remain to be
resolved, based substantially on the character and extent of
poleward return of the outflow boundary from the leading activity.
As such, further modifications (some substantial) may be needed to
especially western parts of the outlook areas today.  One zone of
relatively maximized deep ascent appears to be associated with
passage of the convectively reinforced prefrontal boundary over
parts of MO and southeastern KS, initially penetrating outflow air
from the leading activity.  This regime should continue to benefit
from large-scale DCVA/ascent aloft, related to the shortwave trough
and closely associated convectively induced/enhanced vorticity
fields.  Activity interacting with the outflow boundary`s theta-e
gradient, backed near-surface winds, and maximized mesoscale
vorticity in low levels should pose the greatest potential for
tornadoes.  However the afternoon/evening tornado risk is not yet
focused tightly, due to uncertainties regarding the evolution of a
boundary still being produced at this time.

The general large-scale ascent, along with direct frontal lift and
heating of a very moist airmass in the warm sector, also should
support at least isolated to widely scattered, near-frontal
convective development farther south across parts of AR and eastern
OK, southwest of the outflow boundary.  This activity, including
supercells, should occur in an environment of stronger EML-related
MLCINH for much of the day, but also, steep midlevel lapse rates,
optimal moisture (surface dewpoints commonly low-mid 70s F), and
weakening capping with time this afternoon.  Despite some veering of
near-surface winds, which may limit convergence, any activity that
develops still will occur in an environment of 50-65-kt effective-
shear magnitudes, and peak local MLCAPE commonly in the 3500-4500
J/kg range.  Forecast hodographs and 2D hail models suggest very
large hail of 3+ inches in diameter may occur with any sustained,
relatively discrete storm this afternoon into early evening.
Additional development is possible farther east in the warm sector,
near and east of the Mississippi River and south of the MCS outflow,
off the eastern rim of the EML where MLCINH is weaker but moisture
and heating are strong.

..Edwards/Goss.. 05/26/2024

$$