SPC AC 151929

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0229 PM CDT Sun Sep 15 2024

   Valid 171200Z - 181200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR THE HIGH
   PLAINS...

   ...SUMMARY...
   Strong to locally severe thunderstorms will be possible Tuesday
   across a large swath of the High Plains region, mainly from late
   afternoon into the evening. Severe gusts should be the primary
   hazard, though some hail may also be possible.

   ...High Plains...
   A mid/upper-level shortwave trough initially over the eastern Great
   Basin should take on a negative tilt as it advances towards the
   northern High Plains. Deep lee cyclogenesis is expected over
   northeast WY/southeast MT, with a warm front extending
   east-northeast of the low somewhere from eastern MT into the Dakotas
   during the afternoon and evening. This low will advance north
   towards the MT/SK border area by 12Z Wednesday. 

   Large-scale ascent will be pronounced within this synoptic regime,
   with favorable upper-level difluence, mid-level height falls, and
   low-level convergence. However, weak buoyancy and modest mid-level
   lapse rates will characterize much of the environment to the south
   of the surface low and warm front. Aided by the subtropical moisture
   plume over the Southwest, morning convection near the Four Corners
   region may move across the higher terrain toward the High Plains,
   with additional terrain-driven development possible during the
   afternoon. 

   High-based storms will progress into a well-mixed boundary layer
   that may initially be devoid of appreciable CAPE. This lack of
   greater buoyancy during the late afternoon to early evening (outside
   of areas north of the warm front) yields substantial uncertainty
   regarding the degree of storm organization into the lower
   elevations. But with scattered to widespread convection and
   increasingly extensive outflow expected with time, sporadic severe
   gusts may occur during the afternoon and evening.

   Somewhat more favorable low-level moisture and buoyancy may reside
   near/north of the warm front, from eastern MT into the western
   Dakotas. While stronger ascent and deep-layer flow may not impinge
   upon areas north of the front later in the forecast period, there
   will be some potential for organized convection to develop during
   the evening as the shortwave trough ejects northeastward. A couple
   of supercells and/or stronger clusters will be possible within this
   regime, with a threat of hail and isolated severe gusts. 

   ...Four Corners region...
   Despite the unfavorable time of day, a few strong storms cannot be
   ruled out Tuesday morning across the Four Corners region into
   western CO/NM, in close proximity to the ejecting shortwave trough.
   Wind profiles will be quite favorable for organized convection,
   though it remains uncertain if sufficient buoyancy will be present
   to support any severe threat during the early part of the day. 

   ...Eastern NC/VA...
   With uncertainty already relatively high regarding evolution of the
   currently developing offshore low into D2/Monday, confidence remains
   too low to delineate severe probabilities for D3/Tuesday. Slower and
   more aggressive ensemble members continue to suggest an adequate
   SRH/buoyancy combination for low-topped supercells may linger over
   eastern NC early in the period and shift into parts of eastern VA.
   However, the bulk of guidance still indicates a general weakening of
   the low-level wind field during the day.

   ..Dean.. 09/15/2024

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