Storm Prediction Center Mesoscale Discussion 1317

   Mesoscale Discussion 1317
   NWS Storm Prediction Center Norman OK
   0552 PM CDT Mon Jun 16 2025

   Areas affected...south-central/southeast Montana...east
   Wyoming...and far west South Dakota

   Concerning...Severe potential...Watch possible 

   Valid 162252Z - 170045Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Thunderstorms will continue to increase in coverage this
   evening. Isolated large hail and damaging winds will be possible
   with the strongest thunderstorms. A watch may be needed.

   DISCUSSION...Thunderstorms are developing this afternoon across the
   higher terrain across south-central Montana. These thunderstorms
   have a history of producing severe hail as they move east-southeast.
   Strong effective-shear on the order of 40-50 knots and most-unstable
   CAPE around 1500 J/kg should support a continued threat for at least
   sporadic severe hail.

   To the south, additional thunderstorms have developed across the
   higher terrain of central Wyoming and farther south in southeast
   Wyoming. The environment is more favorable for severe hail/wind here
   than farther to the northwest, with effective-layer shear generally
   at or above 50 knots and most-unstable CAPE on the order of
   2000-3000 J/kg. A recent storm/cluster of storms on the
   Converse-Albany county line has rapidly intensity with MESH values
   in the 1-1.5 inch range. Additional thunderstorm development is
   expected this afternoon/evening.

   The expected evolution of these two clusters is to eventually merge
   together across northeast Wyoming and push into western South Dakota
   later this evening. Buoyancy across South Dakota looks weaker than
   areas farther west and a general decrease in thunderstorm intensity
   is expected through the loss of diurnal heating and movement into a
   slightly more stable environment. 

   Current expectation is that a watch may be needed given the overall
   environment. However, uncertainty remains as to the potential
   coverage of severe threat along with the eventually evolution/merger
   of these two areas. Trends will continue to be monitored for
   potential watch issuance.

   ..Marsh/Mosier.. 06/16/2025

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

   ATTN...WFO...UNR...CYS...BYZ...GGW...RIW...TFX...

   LAT...LON   42260648 43230880 45341102 46701028 47050800 46450557
               45080320 43570346 43020430 42230443 42140600 42260648 

   MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 95 MPH
   MOST PROBABLE PEAK WIND GUST...65-80 MPH
   MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN