Severe Storm Outlook Narrative (AC)
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985
ACUS11 KWNS 181937
SWOMCD
SPC MCD 181936
MTZ000-IDZ000-182100-
Mesoscale Discussion 1651
NWS Storm Prediction Center Norman OK
0236 PM CDT Sat Jul 18 2026
Areas affected...Western Montana...central Idaho
Concerning...Severe potential...Watch possible
Valid 181936Z - 182100Z
Probability of Watch Issuance...40 percent
SUMMARY...Isolated to widely scattered severe thunderstorms are
expected this afternoon and early evening with a risk for damaging
gusts and large hail. Trends in storm coverage will be monitored and
a Severe Thunderstorm Watch is possible.
DISCUSSION...Isolated strong thunderstorms have developed in the
vicinity of the ID/MT border west or Butte as of 1930z. This area is
along the fringe of somewhat stronger mid-level flow associated with
an upper low over southern British Columbia, and within a plume of
monsoonal moisture along the periphery of an expansive mid-level
ridge. Moderate instability, characterized by MLCAPE of 1000 to 1500
J/kg and 35-45 kts of southwesterly shear will be favorable for
supercell and multicell storm structures. Damaging gusts,
potentially in excess of 75 mph, will be the primary risk. Large
hail is also possible with any persistent supercell.
The primary uncertainty is storm coverage, and trends will continue
to be monitored for the possibility of a Severe Thunderstorm Watch
this afternoon.
..Bunting/Thompson.. 07/18/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...TFX...MSO...
LAT...LON 45571206 45261354 45321433 45411502 45531516 46111510
46611448 46991369 47501273 47721194 47861104 47541065
47211059 46501080 45761175 45571206
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN