SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0749 AM CDT Sat Aug 24 2024
Valid 241300Z - 251200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE FOUR
CORNERS REGION NORTHEASTWARD INTO THE CENTRAL HIGH PLAINS...OVER
PARTS OF MISSOURI TO NORTHERN ARKANSAS...AND ALSO OVER AND NEAR
WESTERN OKLAHOMA...
...SUMMARY...
Strong to locally severe storms are possible today from the Four
Corners region northeastward into the central High Plains, over
parts of Missouri to northern Arkansas, and also over and near
western Oklahoma.
...Synopsis...
Positively tilted mid/upper-level troughing should shift slowly
eastward through the period, from the West Coast States to the
northern Rockies, Great Basin and southern CA. Several shortwaves
will pivot through the associated tightly cyclonic regime astride
the trough, then eject into the downstream southwest flow.
Additional perturbations will move northeastward in continuing
southwest flow over the southern Rockies and central Plains, closer
to a pronounced anticyclone whose 500-mb high should move slowly
northeastward over OK. Ridging accompanying that high should build
northeastward to southern Hudson Bay by the end of the period. A
broad fetch of deep-layer moisture was apparent in moisture-channel
imagery and surface analysis from northwestern MX across the Four
Corners to the central Rockies and adjacent High Plains.
Otherwise, the 11Z surface chart showed a long-lived,
quasistationary frontal zone from Atlantic waters off the Carolinas,
southwestward over northern FL, to coastal LA, then northwestward as
a warm front across southern/western OK to a low near DDC. Rich
moisture has spread through the front over central eastern OK and
into southern/central KS, with upper 60s and greater surface
dewpoints. The low is expected to move/redevelop into the
north-central KS/south-central NE vicinity by 00Z, with warm
frontogenesis to its east across the southern IA/northern NE area.
A separate cold front -- analyzed from eastern MT southwestward over
northwestern UT and southern NV -- should move slowly eastward
through the period, reaching the western Dakotas, central WY and
southwestern UT by 12Z tomorrow.
...Four Corners to Central High Plains...
Again today, the persistent monsoonal moisture plume (somewhat
eastward-displaced from previous days) should host widely scattered
to scattered thunderstorms by mid/late afternoon. Activity should
move northward to northeastward over this corridor, with isolated
severe gusts being the main concern, and hail near severe limits
possible over the High Plains portion of the outlook area.
Diurnal heating of higher terrain from just south of I-40 across the
Four Corners, San Juans, and assorted ranges from there to the
Laramies and Front Range, should remove MLCINH quickly into early
afternoon, fostering deep convective growth. Effective shear will
be modest (generally 30 kt or less) due to a lack of both
1. Stronger/backed near-surface flow and
2. Greater CAPE density and buoyant depth (related to modest lapse
rates aloft in the monsoonal plume).
Still, the southeastern fringe of the mass response in upper levels
to the Western CONUS troughing should yield enough cloud-layer shear
for a few organized multicell storms, with translational vector
augmentation of outflow winds possibly contributing to marginal
severe potential. The main supporting factor for downdraft
intensity will be a well-mixed subcloud layer beneath around 200-800
J/kg ambient MLCAPE.
...MO/AR...
An MCV was apparent in composited radar imagery over southeastern NE
between LNK-FNB, and should pivot slowly southeastward through the
day. Associated regionally enhanced low-level moist/warm advection,
and isentropic lift to LFC, have been supporting swath of elevated
convection now over portions of northwestern MO. Lightning coverage
and cooling IR cloud tops have been noted the past hour in a roughly
north/south-oriented band of embedded thunderstorms, though
radar-reflectivity structures remain messy and disorganized.
Further organization/intensification with a southward translational
thrust is possible through the day, as a combination of surface
heating and boundary-later warm/moist advection combine to
destabilize the foregoing airmass. This will lead to at least
isolated potential for damaging gusts and marginally severe hail.
Guidance still varies considerably on the potential for this
activity to merge upscale enough for a single, well-developed cold
pool, which would create a greater conditional wind threat over
parts of west-central/southwestern MO and perhaps into northern AR
before encountering decreasing instability. Southern parts of the
outlook area have been extended somewhat, and the area widened
somewhat, to account for these mesobeta- to convective-scale
uncertainties.
...Western OK and vicinity...
Isolated to widely scattered thunderstorms are possible from mid-
late afternoon, with a few perhaps straying into early evening,
offering locally strong-severe microbursts.
A surface moist/buoyancy axis will persist under and near the
mid/upper high, across southern to northeastern OK and into eastern
KS. West of the associated moisture plume, an effective dryline
will set up by midafternoon from northwest TX to northwestern OK,
representing a differential between more intense heating/mixing to
the west and the more strongly capped, moist boundary-layer
environment under and nearer the high aloft. That boundary also
should conform closely to a wind-shift line and confluence/
convergence axis, west of which winds at the surface will have a
substantial westerly component. With further westward extent into
the Panhandles, the boundary layer will be too dry to support
substantial convection. Within the transition zone, represented by
the outlook area, just enough moisture should be present to support
a minimally capped, deep, hot, well-mixed boundary layer with around
250-1000 J/kg MLCAPE and DCAPE values commonly 1000-2000 J/kg. the
dryline should retreat northwestward through the area this evening,
but under unfavorably strong (and intensifying) MLCINH, and without
appreciable large-scale support, later development is not expected.
..Edwards/Bentley.. 08/24/2024
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