Storm Prediction Center Mesoscale Discussion 1746

   Mesoscale Discussion 1746
   NWS Storm Prediction Center Norman OK
   0259 PM CDT Mon Jul 21 2025

   Areas affected...portions of central and eastern MT into western
   ND/SD and northeast WY

   Concerning...Severe potential...Watch likely 

   Valid 211959Z - 212200Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Severe thunderstorm potential will increase over the next
   1-3 hours. Potential for large hail 2.5-3.0 inches in diameter,
   damaging gusts to 80 mph, and possibly a tornado will be possible
   into the evening hours. A severe thunderstorm watch is likely for
   parts of the discussion area by 22z.

   DISCUSSION...Isolated thunderstorms and increasing cumulus are noted
   near the higher terrain of northern WY/southern MT. This activity is
   developing within drier air and strong differential heating over
   higher terrain and as increasing large-scale ascent begins to
   impinge on the area from the west. With time, additional convection
   is expected to spread northeast into an axis of great boundary-layer
   moisture in the upper 50s to low 60s F from central MT into the
   western Dakotas. 

   Favorable vertical shear amid a roughly west to east oriented tongue
   of modest to strong instability will support initial cells capable
   of large hail. Steepened low-level lapse rates and at least some
   modest dry air noted in forecast soundings centered around 700 mb
   suggests strong winds also will be possible. This may especially
   occur if any clusters/bows develop as a low-level jet increases
   during the evening, and with eastward into the western Dakotas. As
   storms interact with the moist axis across southeast MT, some
   potential will exist for a tornado or two if capping is sufficiently
   eroded and where backed low-level winds will result in locally
   enhanced 0-1 km SRH.

   Initial severe thunderstorm watch issuance is expected by 22z,
   though eastern extent of watch issuance is a bit uncertain and may
   or may not extend into the western Dakotas with this watch issuance.

   ..Leitman/Smith.. 07/21/2025

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

   ATTN...WFO...BIS...UNR...BYZ...GGW...TFX...

   LAT...LON   44260422 44220359 44340317 44820295 45760286 46920302
               47720348 48090542 47840790 47101010 46681056 46231074
               45551031 45170739 44880570 44260422 

   MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 95 MPH
   MOST PROBABLE PEAK WIND GUST...65-80 MPH
   MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN