429
FXUS65 KMSO 252020
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
220 PM MDT Fri Apr 25 2025

.DISCUSSION...

KEY MESSAGES:

- East winds to continue into this evening, but should end by
  Saturday morning

- Saturday will be the warmest day this week, but chance of
  showers and thunderstorms increase in the afternoon and evening

- Cooler and wetter pattern anticipated by Sunday into Monday.
  Snow accumulations possible above 5000 feet Sunday night into
  Monday morning across southwest Montana

East winds remain in place today and will likely strengthen this
evening into the overnight hours for locations exposed to an
easterly wind direction, such as Missoula valley. Winds are
anticipated to decrease by Saturday morning and trend more south
to southwesterly.

High pressure will begin to break down on Saturday as a low
pressure system moves into the Great Basin and begin to eject
northeastwards. This will set up southwest flow across western
Montana and north central Idaho. Warm temperatures are
anticipated, however increasing moisture will also allow for cloud
cover and showers/thunderstorms by afternoon and evening. Due to
the dry low levels of the atmosphere, showers and thunderstorms
that develop will be capable of winds gusting 30 to 40 mph.

Sunday into Monday will see a marked drop in temperatures as the
upper level low moves into southern Idaho and Wyoming. Forecast
models continue to show the best dynamics and precipitation
favoring the Continental Divide into southwest Montana and Lemhi
County (south of Interstate 90 and east of Highway 93). Middle of
the road forecasts for these areas (25th to 75th percentile) show
48 precipitation amounts ranging from 0.25" to 0.75" by Monday
morning. Further north and west, precipitation will be more
showery in nature which will lead to a large variation in
precipitation amounts.

One concern for this system will be for snowfall to occur into
lower elevations than the forecast currently represents Monday
morning. Climatologically, patterns like this have been know to
produce snow into the valley locations of southwest Montana. While
confidence in this scenario playing out is relatively low (10-20
percent) locations such as Butte, Anaconda and Philipsburg could
potentially receive light snow accumulations by Monday morning,
particularly if the system slows down and moisture phases better
with incoming colder air. Mountain passes (MacDonald, Georgetown
Lake, Homestake, Bannock, etc) have a 60 percent chance of
accumulating snow during this timeframe. If you have travel or
outdoor plans, consider monitoring the forecast this weekend.

Cool, breezy and overall active weather will continue into the
early part of next week. Confidence remains high for ridging to
develop by Thursday-Friday however. This will allow for another
period of warm and dry weather.

&&

.AVIATION... The upper level flow pattern will be transitioning
to southern today as a weak low pressure moves off to the east
and a stronger low pressure moves into to central California. Some
moisture and energy will move northward causing a few showers
across portions of central Idaho into southwest Montana. KSMN has
the best chance of experiencing showers within the vicinity of
the terminal. While the remainder of the terminals should have
fair flying conditions. Easterly winds will remain over western
Montana and north central Idaho, and will likely strengthen some
this evening between 26/0000z and 26/0600z. KMSO and KBTM will
likely feel the brunt of these winds with gusts up to 25 kts.
Saturday will see increasing clouds and showers/thunderstorms
migrating further north by afternoon. Wind gusts to 30 kts will be
possible with convection.

&&

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

$$