SPC AC 271245

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0745 AM CDT Sun Apr 27 2025

   Valid 271300Z - 281200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR MUCH OF THE
   GREAT PLAINS...

   ...SUMMARY...
   Isolated to scattered severe thunderstorms are possible on Sunday
   evening into early morning Monday across parts of the Great Plains.
   Large hail, severe gusts, and a few tornadoes are all possible.

   ...Synopsis...
   Early morning satellite imagery shows modest upper ridging between 
   a pair of well-defined cyclones, one centered over NV and the other
   centered over northern NY/VT. The NV cyclone forecast to shift
   slightly eastward throughout the day as a shortwave trough, and
   associated jet streak, rotate through its base. Moderate to strong
   southwesterly flow associated with this shortwave will spread
   northeastward from the Southwest into central Plains and Mid MO
   Valley. 

   Recent surface analysis reveals an expansive area of high pressure
   centered over the Upper Great Lakes covering much of the eastern
   CONUS. A broad area of low pressure exists over the intermountain
   West, with several embedded lows. A tight surface pressure gradient
   exists between these two features across the Plains, and the
   resultant moderate low-level flow will contribute to northward
   moisture advection throughout the period.

   Any large-scale forcing for ascent associated with the shortwave
   progressing around the NV cyclone will remain west of this better
   low-level moisture (and associated buoyancy) until later tonight,
   when it reaches the northern High Plains. Ample buoyancy and
   moisture will exist across the central and southern High Plains, but
   the lack of stronger large-scale forcing for ascent will result in a
   more conditional severe thunderstorm potential.

   ...Southeast MT...Western Dakotas...
   A deepening lee trough is forecast to result in surface cyclogenesis
   in the far eastern MT/WY border vicinity by late this afternoon.
   Strong boundary-layer mixing is anticipated across the region,
   promoting airmass destabilization but also likely keeping dewpoints
   in the 40s across much of the region. Convergence along several
   boundaries across the region, including a surface trough extending
   across southeast MT and the lee trough along the eastern WY border
   vicinity, amid this destabilized airmass will result in thunderstorm
   development, particularly during the late afternoon/early evening as
   increasing large-scale ascent complements the low-level convergence.

   An eastward storm motion should take any storms that develop in
   better low-level moisture over time, with a strengthening low-level
   jet helping to maintain favorably moist low-level inflow. Even with
   this modest improvement in thermodynamics, nocturnal stabilization 
   should result in storms becoming more elevated over time. Primary
   threat across this region are large hail and damaging gusts. 

   ...Central/Southern High Plains...
   Mid 60s dewpoints are already in place across the Permian Basin and
   the general expectation is for low-level moisture to increase
   throughout the day. 60s dewpoints will likely be in place across all
   but far western KS by 21Z and into much of central NE by 00Z. Strong
   heating is anticipated across this region as well, resulting in an
   area of moderate to strong buoyancy from southwest NE into west TX
   by the late afternoon. Large-scale forcing for ascent across the
   region will be nebulous, but low-level convergence along the dryline
   amid little to no convective inhibition may result in convective
   initiation. 

   With dryline convergence as the mechanism for convective initiation,
   predictability is low and convection-allowing guidance has limited
   utility. Dryline circulations will likely be strongest across the TX
   Panhandle/West TX where temperatures west of the dryline will be
   warmest, but low-level coverage will likely maximize in the CO/NE/KS
   border intersection vicinity near a developing surface low. As a
   result, these two areas may have a greater risk for thunderstorms
   today. 

   The overall environment will be very supportive of supercells with
   any storms that do form, with large to very large hail as the
   primary risk initially. Strong downdrafts are possible as well. A
   westward shift of the dryline and strengthening low-level jet will
   support an increase tornado threat during the evening with any
   storms that persist (or develop along the retreating dryline). The
   kinematic environment improves notably across the TX Panhandle,
   western KS, and western NE between 00Z and 06Z, so any storms that
   are ongoing may be able to organize considerably before eventually
   weakening due to nocturnal stabilization.

   ..Mosier/Broyles.. 04/27/2025

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