495
FXUS65 KMSO 101751
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
1151 AM MDT Mon Aug 10 2026

.DISCUSSION...

KEY MESSAGES:

-  Widespread smoke continues to degrade air quality, with the
   highest impacts across northwest Montana

-  Elevated to near-critical fire weather across Southwest Montana
   today and Tuesday.

-  A gradual cooling trend by the middle of next week; rain and
   thunderstorm chances, primarily along the Continental Divide.


Air Quality & Smoke (Through Tuesday)

Dry, westerly flow aloft will maintain widespread wildfire smoke
and degraded air quality across the region through Tuesday.
Current observations report air quality indexing in the unhealthy
to very unhealthy range, primarily along and north of the
Interstate 90 corridor. Upstream conditions offer little immediate
relief, as active wildfires across Washington and Oregon continue
to transport smoke into the Northern Rockies. Diurnal inversions
will trap smoke near the surface overnight, though afternoon
boundary layer mixing and ventilation should afford temporary,
minor improvements each afternoon if there is clear air aloft to
mix into.

Fire Weather (Through Tuesday)

Hot, dry, and breezy conditions will drive elevated to localized
critical fire weather conditions, focused along and east of the
Continental Divide in southwest Montana. The highest probability
(40-50%) for Red Flag criteria remains localized near Dillon,
where afternoon wind gusts of 20-30 mph will overlap with low
relative humidity.

Cooling Trend & Moisture Surge (Wednesday-Thursday)

A change begins Wednesday as an upper-level trough crosses over
the Pacific Northwest. Showers and thunderstorms will initially
form along the US/Canada border and the Continental Divide
Wednesday before expanding across the region by Thursday. This
shift is driven by a deep south-southwest flow drawing a plume of
monsoonal moisture northward. Primary hazards include gusty,
erratic outflow winds, lightning creating new fire starts, and
localized heavy rainfall by Thursday as precipitable water values
increase near 1 inch. There are hints that instability could be
marginal thus limiting thunderstorm coverage, especially if smokes
limits daytime heating. Concurrently, model guidance indicates a
surface cold front driving southward along the Divide Wednesday
morning but stalling out in northwest Montana. A strong push
Wednesday night into Thursday morning will generate a north-
northeast wind shift for much of western Montana that may yield
temporary relief from dense smoke with moderate confidence at this
point.

Extended Outlook (Friday Through Weekend)

A prevailing southwest flow regime will keep thunderstorm chances
elevated primarily across southwest Montana through the weekend,
with isolated activity persisting farther north. Model sounding
indicate drying of the low-levels, allowing gusty outflow winds to
be a concern once again.

&&

.AVIATION...Wildfire smoke will remain the primary operational hazard
through Tuesday, maintaining surface visibilities between 2 and 6
SM. The most persistent visual degradation will concentrate
across northwest Montana, north of the Interstate 90 corridor.
Westerly surface winds will gust 15-20 kt each afternoon before
boundary-layer decoupling leads to rapid weakening around sunset.
In addition, high density altitude concerns will persist across
higher- elevation terminals during peak afternoon and early
evening heat.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...&&

$$