Storm Prediction Center Mesoscale Discussion 1355

   Mesoscale Discussion 1355
   NWS Storm Prediction Center Norman OK
   0547 PM CDT Sat Jun 27 2026

   Areas affected...parts of the western Dakotas

   Concerning...Tornado Watch 406...

   Valid 272247Z - 280045Z

   The severe weather threat for Tornado Watch 406 continues.

   SUMMARY...The risk for supercells capable of producing sizable hail
   and increasing potential for a couple strong tornadoes is probably
   highest between now and 6-7 PM MDT.

   DISCUSSION...Strong thunderstorm development is now well underway
   within clusters  developing north and northeast of the Big Horn
   Mountains, and within  deep surface troughing, near the northeastern
   Montana international border.  More recent, and still discrete,
   storm initiation has been occurring in the vicinity of the surface
   trough axis near the southeastern Montana/Dakotas state border
   through western South Dakota to the north of the Black Hills. 
   Immediately to the north and east of the latter activity,
   boundary-layer instability is currently maximized in a narrow
   corridor and appears to include CAPE in excess of 3000 J/kg. 

   Prior to the arrival of consolidating and strengthening outflow
   emanating from the upstream convection, there appears a couple of
   hour window for intensifying discrete storm development, in the
   presence of strong deep-layer shear beneath 40-50 kt southerly flow
   around 500 mb.  Some further strengthening of south-southeasterly
   flow around 850 mb through 00-01Z may contribute to enlarging
   clockwise-curved low-level hodographs increasingly conducive to the
   development of tornadoes, in addition to large hail and localized
   strong downbursts.

   ..Kerr.. 06/27/2026

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

   ATTN...WFO...ABR...BIS...UNR...

   LAT...LON   45840350 46200350 46740357 47460386 47720339 47360277
               46960220 46110128 44810162 44490194 44650237 45410301
               45840350 

   MOST PROBABLE PEAK TORNADO INTENSITY...120-145 MPH
   MOST PROBABLE PEAK WIND GUST...75-90 MPH
   MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN