SPC AC 260556

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1256 AM CDT Wed May 26 2021

   Valid 261200Z - 271200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE CENTRAL PLAINS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   MODERATE RISK INTO THE SOUTHERN PLAINS AND ACROSS THE NORTHEASTERN
   US...

   ...SUMMARY...
   Severe thunderstorms will spread across the central Plains during
   the late afternoon and evening with a threat for large and
   destructive hail, very damaging winds, and tornadoes. Scattered
   severe is also expected across the southern High Plains and much of
   the northeastern US where damaging winds are the primary concern.

   ...Central/southern Plains...

   Early this morning a well-defined upper trough was located over
   eastern WA/OR. This feature is forecast to translate into eastern
   MT/WY by 27/00z with diffluent high-level flow expected to spread
   across the northern High Plains region during the afternoon. In
   response, a surface low should develop over southern WY by 18z then
   settle southeast along a frontal zone draped across the central
   Plains. Favorable low-level trajectories across KS/southern NE will
   force higher boundary layer moisture into the NE Panhandle prior to
   forecast maximum temperatures. In fact, isolated supercells will
   likely initiate across parts of eastern WY along the western fringe
   of higher-moisture content where large-scale forcing will be
   maximized. Latest thinking is boundary-layer heating will be most
   intense across southeast WY/southern NE Panhandle, south along the
   NM/TX border region. NAM forecast sounding for BFF at 21z exhibits
   around 3000 J/kg MLCAPE with surface-6km bulk shear on the order of
   40kt. Environmental conditions appear very favorable for discrete
   supercells early in the convective cycle ahead of the surface low
   into northeast CO. With time, numerous supercell structures should
   grow upscale as they mature along/south of the aforementioned
   frontal zone. Very large hail will likely be noted with this early
   activity, and SRH values certainly suggest tornadoes will be a
   threat until storm mergers lead to a potentially significant MCS
   downstream over southern NE/northern KS. If an intense MCS does
   evolve, as seems possible, very damaging winds could be noted along
   the leading edge of this cluster as it surges east-southeast along
   the nose of a pronounced LLJ.

   Isolated severe thunderstorms will also develop south across the
   High Plains into west TX where strong afternoon heating will once
   again allow surface parcels to reach their convective temperatures
   by late afternoon. Modest southwesterly flow aloft will support
   supercells, and large hail/wind are the greatest risks along the
   southern dryline.

   ...Northeast...

   Moist plume characterized by PW values in excess of 1.5 inches
   currently extends across the lower MS/lower OH Valley into lower MI.
   Deep trajectories appear favorable for some of this moisture to be
   drawn northeast across the OH Valley into southern QC ahead of the
   primary front that will approach the international border by early
   evening. However, strong boundary-layer heating will be observed
   well ahead of the front where moisture content should be slightly
   drier, but noteworthy and sufficient for robust convection. Only
   minor changes have been made to earlier severe probabilities across
   this region and that is to extend the SLGT Risk south into VA where
   higher moisture content/stronger instability will be noted.

   Forecast soundings suggest scattered thunderstorms may develop
   across upstate NY, southwest across western PA into eastern OH by
   16-17z as surface temperatures warm through the 70s to near 80F.
   This activity will then spread/develop east across the Hudson Valley
   into portions of New England. Farther south, surface temperatures
   should warm into the upper 80s across the Delmarva region and this
   higher buoyancy may result in a greater risk of hail from eastern PA
   into northern VA as thunderstorms develop a bit later during the mid
   afternoon. Otherwise, damaging winds will likely be the greatest
   risk with multicellular updrafts that intensify during the heat of
   the day ahead of the short-wave trough.

   ..Darrow/Wendt.. 05/26/2021

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