Storm Prediction Center Mesoscale Discussion 1642

   Mesoscale Discussion 1642
   NWS Storm Prediction Center Norman OK
   0312 PM CDT Fri Jul 17 2026

   Areas affected...West and southwest Montana and extreme northeast
   Idaho

   Concerning...Severe potential...Watch unlikely 

   Valid 172012Z - 172215Z

   Probability of Watch Issuance...20 percent

   SUMMARY...Scattered thunderstorms are expected to form through
   mid-late afternoon with a gradual increase in the threat for
   isolated severe outflow gusts and large hail.

   DISCUSSION...Visible satellite imagery reveals deepening convection
   over the high terrain across southwest and western MT where surface
   temperatures have warmed well into the 80s with dewpoints in the
   mid-upper 50s.  The 18z soundings from TFX and BOI suggest that
   surface temperatures need to warm to 90+ F to eliminate convective
   inhibition for the lower elevations, though inhibition has
   diminished over the higher terrain.  Though forcing for ascent will
   remain subtle, there are embedded perturbations rotating northward
   over ID/western MT around the northwest periphery of the midlevel
   ridge.  These perturbations, in combination with additional surface
   heating, will support scattered thunderstorm development the next
   few hours.  Steepening low-level lapse rates will favor
   strong-severe outflow gusts as the main threat in an environment
   with moderate buoyancy.  Isolated large hail may also occur with any
   more organized/supercell storms, given effective bulk shear of 30-35
   kt.

   ..Thompson/Guyer.. 07/17/2026

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

   ATTN...WFO...BYZ...TFX...MSO...OTX...

   LAT...LON   46011013 45580943 45210931 45080955 45271109 45631269
               45671368 46071469 47121509 48091510 48921488 48951402
               48931310 47981257 47041194 46431126 46011013 

   MOST PROBABLE PEAK WIND GUST...55-70 MPH
   MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN