Mesoscale Discussion 1547
   NWS Storm Prediction Center Norman OK
   0321 PM CDT Tue Aug 17 2021

   Areas affected...Southern to Southwest Montana

   Concerning...Severe potential...Watch unlikely 

   Valid 172021Z - 172215Z

   Probability of Watch Issuance...20 percent

   SUMMARY...Isolated to scattered thunderstorms may be capable of
   severe downburst winds across southwest to southern Montana this
   afternoon and evening. However, this threat will most likely remain
   too isolated to warrant a watch issuance.

   DISCUSSION...A few deeper convective towers with occasional
   lightning have emerged from a growing cumulus cluster over the
   terrain of the ID/MT border over the past hour. This is likely the
   result of increasing instability (MUCAPE values up to 1000 J/kg) and
   strengthening lift over the region as a surface low slowly deepens
   ahead of an approaching upper-level wave. As forcing for ascent and
   instability continue to increase through the late afternoon
   thunderstorm development will become more likely. Downstream of this
   cluster, temperatures across southern MT have warmed into the upper
   80s ahead of an approaching cold front. Additional boundary-layer
   heating/mixing will help further steepen low-level lapse rates to
   near 9 C/km, which may already be achieved at a few sites where
   dewpoint depressions near 40 F are noted. Strong flow aloft may
   support some initial storm organization, and the low-level
   thermodynamic profiles will support a severe downburst potential
   with any strong thunderstorm. Scattered storm coverage is possible,
   but the combination of the approaching cold front and patchy cloud
   cover may spatially limit favorable boundary-layer profiles and the
   subsequent severe wind potential. Because of this limitation, a
   watch is not expected at this time.

   ..Moore.. 08/17/2021

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

   ATTN...WFO...BYZ...GGW...RIW...TFX...PIH...MSO...

   LAT...LON   44891329 45401361 45921327 46921100 47470836 47440716
               47150647 46440652 45440717 45120810 44511151 44421218
               44531281 44891329