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SPC AC 221629
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1129 AM CDT Mon May 22 2023
Valid 221630Z - 231200Z
...SUMMARY... Isolated to scattered severe thunderstorms are most likely in the northwest Texas vicinity, centered on 3 to 10 PM CDT. Large hail and severe wind gusts will be the primary hazards.
...TX/OK Panhandles to the Lower Pecos Valley... An MCV over southwest KS will drift quite slowly east-southeast through tonight. Modestly enhanced westerly mid-level flow (25-30 kts at 500 mb) will be displaced to the south of this MCV, centered across the southern TX Panhandle to the Permian Basin. Cloud coverage is most pronounced close to the MCV, with robust boundary-layer heating expected from the central/southern TX Panhandle southward towards the Pecos Valley. This heating will be coincident with the northwest extent of upper 50s to lower 60s surface dew points and the eastern extent of the elevated mixed layer, supporting moderate buoyancy with MLCAPE of 1500-2000 J/kg. Scattered thunderstorms should develop towards mid-afternoon across the eastern Panhandles into the South Plains, with more isolated activity into the Trans-Pecos.
Within the belt of enhanced mid-level flow, adequate effective bulk shear (from 30-35 kts) and 0-3 km SRH should exist for a few slow-moving supercells. Flow will largely remain neutral to decreasing with height above the mid-levels north of the Permian Basin. A mix of transient supercells and multicell clusters can be expected, with a tendency for upscale growth along consolidating outflows by early evening as a modest increase in low-level warm theta-e advection occurs. Overall setup should favor isolated to scattered large hail from quarter to golf ball size and 50-70 mph wind gusts. Any MCS this evening in the western north TX vicinity should weaken after sunset as it impinges on increasing MLCIN to its southeast.
...MT... An upper-level trough will largely remain anchored over the Canadian to the northern U.S. Rockies during the period, with an embedded shortwave impulse rotating through north ID/northwest MT to the southern British Columbia/Alberta region this afternoon. An attendant surface cold front will push eastward across western MT and serve as a focus for isolated to scattered high-based thunderstorm development.
Boundary-layer dew points from the mid to upper 40s suggest MLCAPE will remain weak from 500-1000 J/kg. Stronger mid to upper-level flow will be displaced west of the front, and as convection develops it will further outpace the better flow given the track of the embedded shortwave impulse. As such, isolated severe hail is possible mainly early. A few outflow-dominated multicell clusters should become the predominant mode with a primary threat of scattered strong to isolated severe wind gusts.
...FL and Northeast Gulf Coast... A minor mid-level impulse will drift slowly east over MS/AL, with a diffuse west/east-oriented quasi-stationary front to its southeast. Scattered thunderstorms are already ongoing along and just north of this front across south GA into extreme north FL. Additional thunderstorms will develop shortly along the sea breezes down the Peninsula, with numerous colliding convective outflows expected later this afternoon.
Mid-level lapse rates will remain weak south, and more moderate to the north, with lower-level winds also remaining weak area wide. Pockets of scattered to broken cloud coverage in the Peninsula and separately over the FL Panhandle into south AL will support steeper low-level lapse rates that will favor sporadic strong to severe outflow gusts of 45-60 mph. Isolated, marginally severe hail will also be possible, mainly with any cells that can be rooted on southwest to south-moving outflows.
..Grams/Lyons.. 05/22/2023


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