916
FXUS65 KMSO 181838
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
1238 PM MDT Tue Aug 18 2026

.DISCUSSION...

KEY MESSAGES:

-  Shower and thunderstorm activity will continue this afternoon.

-  Ridge of high pressure Wednesday through Friday causing warming
   and drying.

-  Increased atmospheric moisture leading to a return to active
   weather Friday onward.

A disturbance moving through the Northern Rockies will interact
with a drier air mass. Thunderstorms will not be widespread but
areas that may see isolated storms will be along the Continental
Divide, especially Silver Bow County and east of the Divide. Due
to drier air mixing down to the surface the main threat will be
strong outflow winds, with a 5% or less chance of a storm
attaining severe strength (wind gusts in excess of 58 mph) in the
vicinity of Silver Bow County.

The driest day of this air mass change will be Wednesday as
relative humidities lower into the teens. Please exercise caution
with any outdoor flames and consult local government as many
locales have instituted some level of burn ban.

This air mass will also produce a warm up with Thursday and
Friday being the warmest days of the forecast period. Hells Canyon
ID, temperatures will warm 105 to potentially 110F during this
period, so take it easy with those outdoor activities. Elsewhere,
its not much better with widespread 90s.

A trough will deepen off the west coast, pulling up a tropical air
mass on Friday into the weekend. Expect relative humidities to
increase. The question now becomes at what level in the atmosphere
will the moisture reside. Currently, most of the moisture will be
high based, so is the response simply clouds and cooler (current
forecast), some showers forced by the mountains, or widespread
precipitation. This answer will likely come into focus as high
resolution models have some input, 72-hours or less from the
system. A return to daily afternoon thunderstorms is a most likely
solution, Sunday through Tuesday, with some question as to the
extent of coverage.

&&

.AVIATION...A disturbance will be moving through the Northern
Rockies today. A few showers are developing across northwest
Montana which could have an impact at KGPI. After 18/2000z, more
showers and thunderstorms will develop mainly across northwest and
southwest Montana. Unlike previous days these storms will be
capable of strong outflow winds which could impact area terminals.
KGPI, KBTM and KSMN have the best potential to be impacted by
these storms this afternoon and evening.

&&

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

$$