Mesoscale Discussion 1183
   NWS Storm Prediction Center Norman OK
   0303 PM CDT Wed Jul 07 2021

   Areas affected...south central Montana

   Concerning...Severe potential...Watch possible 

   Valid 072003Z - 072200Z

   Probability of Watch Issuance...60 percent

   SUMMARY...Severe storms, including a few supercells, are forecast to
   develop north of a warm front with a risk for damaging winds and
   hail into this evening. A weather watch may be needed.

   DISCUSSION...Downstream of a shortwave trough across the Pacific
   Northwest, showers and a few thunderstorms have developed across
   portions of western Montana and eastern Idaho. As additional
   lift/destabilization develops ahead of the approaching trough,
   convective coverage/intensity should increase late this afternoon
   and early this evening. Warm and moist surface conditions with T/TDs
   in the 80s/50s F respectively are contributing to between 500 and
   1000 J/kg of MLCAPE across much of Montana. While some inhibition
   remains, it should reach diurnal minimum over the next couple of
   hours coincident with increased forcing for ascent from the trough
   aloft. Additional storm development appears increasingly likely by
   21-23z within a moderately sheared airmass (effective shear 40-50
   kts). Supercells and short line segments appear to be the dominant
   storm mode as high-based convection moves out of the mountains into
   deeper moisture and becomes better organized. With steep low and
   mid-level lapse rates in place, damaging wind gusts and severe hail
   will be the primary threats. Later this evening, upscale growth into
   one or two convective clusters/line segments may present an enhanced
   corridor of wind damage potential downstream across portions for
   central and eastern Montana. Here, greater vertical shear may
   support a more organized storm mode capable of strong wind gusts, a
   few of which could be significant. 

   Convective trends are being monitored for a possible weather watch 
   around the 22-00z time frame.

   ..Lyons/Guyer.. 07/07/2021

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

   ATTN...WFO...BYZ...GGW...TFX...

   LAT...LON   46020538 45490735 45480892 45371062 45401092 46021187
               47021189 47571091 47830964 47980739 47980715 47920674
               47640573 47300534 46640513 46020538