ACUS01 KWNS 221255
SWODY1
SPC AC 221254
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0754 AM CDT Thu Aug 22 2024
Valid 221300Z - 231200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
CENTRAL HIGH PLAINS...
...SUMMARY...
The greatest threat for severe gusts and hail appears to be over
parts of the central High Plains this afternoon and evening.
...Synopsis...
A highly amplified pattern in mid/upper levels will persist through
the period, but with some weakening noted for both mean troughing
near the East Coast, and a central CONUS ridge extending northward
from a high over west TX. Southwest flow over the Intermountain
West will strengthen and back somewhat in response to slow
southeastward movement of an intense cyclone -- now centered west of
the northern OR Coast --- while a strong shortwave trough pivots
through its southern semicircle and onshore the northern CA coast by
the end of the period.
Farther east, on the periphery of that southwest flow, a shortwave
trough (with some incorporation of a Sonoran MCV from 24 hours
earlier) was apparent in moisture-channel imagery over northern AZ
and southern UT. This perturbation should eject northeastward over
western CO by 00Z, then into the central Plains overnight, perhaps
with some further convective-vorticity reinforcement then. To the
north, closely spaced shortwave troughs now over south-central SK
and parts of ND/southeastern SK should pivot eastward across the
rest of ND, northern MN and southern/central MB through the period.
At the surface, a quasistationary frontal zone from northern FL
across the northern Gulf Coast, east/north TX and the TX Panhandle
should remain near that position through the period, with the
richest low-level moisture remaining to its south. However, gradual
moisture return of more incompletely modified (yet still
convectively sufficient) character is apparent up the High Plains
from the Panhandles across western NE to the central Dakotas. This
is east of a lee trough over eastern parts of WY/CO, and a weak cold
front analyzed from north-central ND to western SD. The latter
front should proceed eastward across the Dakotas and into
northwestern MN through this evening.
...Central High Plains...
Highly variable thunderstorm coverage is expected over this region,
with the greatest density in the 15%/"slight" area, where upscale
evolution of increasingly outflow-driven thunderstorm clusters
should support severe-gust potential this afternoon into evening.
The primary foci for formation of eventually severe activity should
be the northern Raton Mesa region, Front Range/Sangre de Cristo,
and/or Palmer Divide, with some contribution from the lee trough as
well.
Though far south and east of the stronger flow aloft, sufficient
veering of wind with height is expected to result in effective-shear
magnitude in the 30-40-kt range, indicating potential for some
organized convection. The boundary layer will remain well-heated/
mixed and deep, with very steep lapse rates, even as moisture/
buoyancy increase eastward. With surface dewpoints in the mid 50s
to mid 60s F, peak/preconvective MLCAPE should reach 1500-2000 J/kg
(locally higher) in a corridor near and just east of the longitude
of the CO/KS line. This will foster pulses of strong to isolated
severe gusts in initially discrete to semi-discrete activity atop a
drier boundary layer, becoming better-organized with potential
cold-pool aggregation eastward toward east-central/northeastern CO
and adjoining portions of KS/NE into the higher CAPE. While
specific shape, size, and track(s) of this clustering still depend
on mesoscale details, enough consensus/confidence is now apparent in
the general area of greatest severe-wind potential to ratchet up
unconditional probabilities a level. With MLCINH increasing
eastward from about the KS/CO border longitude and nocturnal
near-surface cooling, the severe threat should weaken eastward from northwestern
KS and southwestern NE tonight.
...Eastern Great Basin and vicinity...
Widely scattered to scattered thunderstorms are possible this
afternoon into early evening, offering strong to isolated severe
gusts and marginally severe hail. After the shortwave trough and
related precip now over parts of this region shifts northeastward,
most of the day should remain for diabatic heating/destabilization
of the higher terrain across the region, with airmass recovery
furthered by warm/theta-e advection from the south. In concert with
available monsoonal moisture, a roughly meridional plume of
essentially uninhibited MLCAPE in the 500-1500 J/kg range should
develop. This will be superimposed under the southeastern rim of
stronger upper flow related to the West Coast troughing/cyclone.
The result should be strengthening cloud-layer shear and some
potential for storm organization, as activity moves generally
northeastward over well-mixed boundary layers.
...Upper Midwest...
A large area of clouds and precip -- with widely scattered embedded
thunderstorms -- should proceed eastward today across the remainder
of eastern ND and parts of northern MN near the international
border. Though the associated lead perturbation now over ND should
be past the area before this afternoon, cyclonic flow aloft should
continue in response to the stronger perturbation farther north,
moving into MB. As such, little if any hindrance to convective
potential is expected from large-scale subsidence, while the
low-level airmass destabilizes diabatically from surface heating
behind the morning activity. Isolated to widely scattered
thunderstorms may develop along/ahead of the cold front, within a
narrow plume of 1000-2000 J/kg MLCAPE supported by 60s F surface
dewpoints. Modest low/middle-level flow is expected, through enough
veering with height should develop to support effective-shear
magnitudes locally near 35 kt. The strongest cells may produce
marginally severe hail or gusts, before convection weakens this
evening.
..Edwards/Mosier.. 08/22/2024
$$
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