628
FXUS65 KMSO 210837
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
237 AM MDT Fri Aug 21 2026

.DISCUSSION...

KEY MESSAGES:

-  Dry conditions with abnormally hot temperatures peaks today
   with elevated dry thunderstorms possible in the afternoon
   through the overnight.

-  Thunderstorms Saturday pose marginal risks for severe-strength
   winds across the region and excessive rainfall in SW Montana
   and NC Idaho.

-  Elevated to near-critical fire weather on Sunday due to gusty
   west winds accompanied by a very dry airmass.

High pressure remains in control over the Northern Rockies
allowing for intense daytime heat that will peak this afternoon across
the region. A rapidly growing wildfire near Happys Inn is pushing
a plume of smoke to the east and northeast which may create
reductions in visibility and air quality through the day today
especially in the Flathead Valley and Glacier National Park.

Elevated monsoonal moisture will creep into Lemhi County and
southwest Montana later this afternoon triggering high-based
showers and dry thunderstorms capable of erratic convective
outflow wind gusts of 30 to 45 mph. This convection pushes
northward overnight into Saturday morning bringing nocturnal dry
lightning and outflow risks along with it into the rest of western
Montana.

An upper-level trough is still on track to lift out of the Pacific
Northwest and phase with increasing monsoonal moisture on
Saturday. Widespread shower and thunderstorm activity will
increase through the afternoon and evening hours across the
region. The Storm Prediction Center has place most of western
Montana and north-central Idaho under a marginal risk for severe
thunderstorms with damaging wind gusts being the primary threat.
Where PWATS are forecast to near and exceed 1.0 inches in
southwest Montana and Lemhi County on Saturday, a marginal threat
for excessive rainfall, due to intense precipitation rates, also
exists. Normally vulnerable spots such as burn scars, urban areas,
and within steep terrain bear increased attention for flash
flooding.

A cold front crosses through, from the west, Saturday evening
into Sunday subduing convection from west to east and lowering
daytime high temperatures by 10-15 degrees; closer to seasonal
normals. However, the post-frontal environment will also bring
deep mixing, strong westerly winds, and a very dry airmass
creating elevated to near-critical fire weather conditions
especially considering the preceding risk of new lightning starts
and holdovers from Friday and Saturday`s convection.


&&

.AVIATION...High pressure will maintain hot conditions and
elevated density altitudes across the regional airspace today. A
newfound fire near Happy`s Inn is producing a significant plume of
smoke that may impact visibilities to points east and northeast of
the fire including KGPI. Elevated convection developing around
and after 21/2000Z near KSMN and KBTM will spread northward into
the evening and overnight bringing the risks of erratic outflow
wind gusts of 25-40 knots, inducing low-level turbulence, and
LLWS near these high-based storm cores. Widespread shower and
thunderstorm activity on Saturday poses threats for strong to
severe wind gusts, hail, and temporary MVFR/IFR weather conditions
across the region particularly during the afternoon hours.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...Heat Advisory from 11 AM this morning to 8 PM PDT this evening
     for Lower Hells Canyon/Salmon River Region...
     Orofino/Grangeville Region.

&&

$$