SPC AC 221948

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0248 PM CDT Mon May 22 2023

   Valid 222000Z - 231200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
   NORTHWEST TEXAS VICINITY...

   ...SUMMARY...
   Isolated to scattered severe thunderstorms are likely across the
   Oklahoma/Texas Panhandles into northwest Texas through late evening.
   Large hail and severe wind gusts will be the primary hazards.

   ...Southern High Plains...
   The previous forecast largely remains on track with only minor
   adjustments needed. Wind probabilities were adjusted slightly to
   account for where convective initiation is occurring and confidence
   in the downstream wind threat is correspondingly higher. See MCD
   #838 for additional details on the near-term forecast.

   ...MT...
   Across MT, the initial convection noted in MCD #837 has demonstrated
   periods of organization with a bowing segment approaching the Great
   Falls, MT area. However, this segment has not maintained consistent
   intensity per GOES IR imagery over the past 1-2 hours, and
   downstream buoyancy remains uncertain. Confidence in a more
   widespread wind threat remains too limited for higher probabilities,
   but a few additional strong/severe storms remain probable.

   ..Moore.. 05/22/2023

   .PREV DISCUSSION... /ISSUED 1129 AM CDT Mon May 22 2023/

   ...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.

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