118
ACUS01 KWNS 251250
SWODY1
SPC AC 251249

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0749 AM CDT Tue Jun 25 2024

Valid 251300Z - 261200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
CENTRAL PLAINS AND MIDWEST...

...SUMMARY...
Damaging wind gusts and large hail are possible across parts of the
central/southern Great Plains and Midwest, late this afternoon and
evening.

...Synopsis...
In mid/upper levels, an initially zonal pattern from the northern
Rockies to the Great Lakes will amplify through the period.  This
will occur as ridging builds over the northern Rockies ahead of a
strong synoptic-scale trough that will move ashore in the Northwest
day 2.  Downstream, a shortwave trough was evident in moisture-
channel imagery aligned nearly west-east over the southern Canadian
Prairie Provinces.  The middle/western parts of this trough should
cross the international border around 00Z, then assume more
meridional tilt overnight.  By 12Z, the trough should extend across
portions of Lake Superior, northern WI, southern MN, and
southeastern SD.  A separate, smaller and weaker perturbation -- now
apparent over southeastern WY -- should move slowly east-
southeastward across NE to the TOP/STJ vicinity by the end of the
period.  Elsewhere, a 500-mb high should strengthen over NM, with an
MCV from earlier Mexican convection moving northwestward across
parts of southern/western AZ.

At the surface, the 11Z analysis showed a low over southwestern WI,
with warm front southeastward over southern Lake Michigan, then
southward over western IN, and a cold front across central parts of
IA/NE.  By 00Z, the cold front should extend from parts of Lower MI
across central IA to a weak frontal-wave low over eastern NE, then
southwestward over southwestern KS.  By 12Z, the front should move
to southern parts of IL/IN, central MO, eastern KS, and southeastern
CO, with weak low(s) over parts of the lower Missouri Valley region.

...Central/northern Plains to Midwest...
Earlier separate complexes of convection have merged into a lengthy
corridor of thunderstorms from parts of southern Lower MI across the
warm front to northern IL.  See SPC Severe Thunderstorm Watch 456
and related mesoscale discussions for near-term guidance on this
activity, most of which generally should diminish into late morning
as it moves into weaker magnitudes of both low-level theta-e and
mid/upper support.  The trailing/western part may persist into
midday or early afternoon, as diurnal destabilization and moist
advection boost buoyancy across eastern parts of the outlook area.
The main concern should continue to be damaging gusts, with isolated
large hail also possible mainly from any relatively discrete cells.

Though mid/upper support should remain modest over the central
Plains to mid Mississippi Valley today, with the Canadian shortwave
trough still well north of the area, weak large-scale lift is
possible ahead of the smaller WY perturbation as it approaches.
Meanwhile, the airmass near the front, and near the western part of
the outflow boundary from the morning MCS activity, should attain
strong heating and evapotranspiratively aided surface dewpoints in
the upper 60s to low 70s F.  By mid/late afternoon, with steep
midlevel lapse rates, a corridor of 3000-4500 J/kg MLCAPE should
develop from parts of northern IL across IA and eastern NE, perhaps
into southern SD.  Lift east and northeast of the surface low, in
the frontal zone, should contribute further to relatively weak
MLCINH and convective potential.

From late afternoon into early evening, favorable parameters should
be relatively maximized, amid 35-40 kt effective-shear magnitudes.
This will support organized multicells, a few supercells, and
merging/clustering of convection into one or more southward to
southeastward over the lower Missouri and mid Mississippi Valley
regions.  With time and upscale organization this evening, an early
mixed-mode/mixed-hazard threat should evolve toward damaging gusts.
Specific areas for development in the high-CAPE corridor still
appear uncertain due to weak low-level flow and the subtlety of
associated forcing.  The threat is far from uniform across the
15%-severe probability area, but mesoscale uncertainties preclude
finer-scale refinement at this time.  More-isolated post-frontal
convection may pose a marginal hail/wind threat over parts of the
Dakotas in post-frontal, but still sufficiently moist/unstable flow
as well, beneath a strip of ascent aloft that precedes the northern
trough.

...Southern Plains...
Ahead of the front, most likely along a surface trough from southern
KS across northern/western OK to the TX Panhandle, isolated to
widely scattered thunderstorms are possible late this afternoon
through early evening.  Isolated severe gusts and hail will be
possible.  Hot surface temperatures, a deeply well-mixed boundary
layer, and still enough low-level moisture will remain to support
uninhibited buoyancy, with MLCAPE in the 1000-2000 J/kg range.
Despite veering of winds with height, weak low/middle-level winds
will dampen vertical shear, except for some strong upper/anvil-level
flow aiding ventilation high aloft.  Being strongly tied to daytime
heating, this activity should weaken and diminish considerably after
about 03Z.

..Edwards/Mosier.. 06/25/2024

$$