Storm Prediction Center Mesoscale Discussion 1306

   Mesoscale Discussion 1306
   NWS Storm Prediction Center Norman OK
   0727 PM CDT Sun Jun 15 2025

   Areas affected...northeast Wyoming and western half of South Dakota

   Concerning...Severe potential...Watch likely 

   Valid 160027Z - 160200Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Thunderstorms capable of producing large hail and damaging
   winds will continue to develop this evening across Wyoming before
   spreading east into South Dakota. A Severe Thunderstorm Watch will
   be needed shortly.

   DISCUSSION...Thunderstorms are increasing in coverage and intensity
   this evening across portions of northeast Wyoming. This appears to
   be in response to increased ascent from the approaching shortwave
   trough and a strongly buoyant and sheared atmosphere. (This
   evening's observed Rapid City, SD, sounding has nearly 2700 J/kg of
   most-unstable CAPE and 35 knots of effective-layer shear.)

   Thunderstorms will continue to intensify and increase in number this
   evening within this environment. With time, expectation is to
   develop one or more clusters/bowing segments that should move
   east-northeast out of Wyoming and into western South Dakota. After
   this, guidance is split as to whether these potential bowing
   segments remain discrete or interact/merge with potential MCSs
   across both North Dakota (from the Montana thunderstorms within
   Severe Thunderstorm Watch #418) and southern South Dakota/northern
   Nebraska (associated with a potential MCS within Severe Thunderstorm
   Watch #420).

   Damaging winds and large hail will be possible initially, with a
   tendency to favor an increasing wind threat with time.

   ..Marsh/Smith.. 06/16/2025

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...ABR...LBF...UNR...CYS...BYZ...RIW...

   LAT...LON   42630493 43110634 44800545 45840222 45089987 43170051
               42630493 

   MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 95 MPH
   MOST PROBABLE PEAK WIND GUST...75-90 MPH
   MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN