199
FXUS65 KMSO 202017
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
217 PM MDT Sun Apr 20 2025

.DISCUSSION...

KEY MESSAGES:

- Snow over mountain passes on Monday morning.

- Unsettled spring-like weather will continue into the middle of
  next week with a warm-up later in the week.


Some instability this afternoon is leading to isolated convective
showers over western Montana. Some of these showers are producing
lightning strikes. Although convection will wrap up early this
evening, unsettled weather in the form of more widespread
precipitation will continue. A trough of low pressure over western
Canada will dig southward this evening into the Northern Rockies.
This system, along with an associated cold front, will keep valley
rain and mountain snow in the forecast through Monday. Snow levels
will drop below about 4000 tonight. Motorists should expect a few
inches of snow for Lookout, Lolo, Lost Trail, and Marias passes
for the Monday morning commute. Moist northwesterly flow will
bring continued mountain showers on Tuesday, especially for
northwest Montana east of about Highway 93, the Idaho-Montana
border, and the Clearwater range. The position of an upper level
jet streak and an unstable atmosphere will be conducive to windy
conditions during the day Monday as well. Those venturing to the
higher terrain will experience ridgetop gusts of 30-40 mph.

The forecast for late Wednesday is showing some uncertainty. Most
solutions (about 75%) are showing a fast-moving open wave
bringing scattered showers to southwest Montana and Lemhi County.
The remaining 25% of solutions are showing a mid-level low
pressure circulation over northwest Wyoming. This second solution
would be capable of moderate winter travel impacts for Lemhi
County and southwest Montana including Homestake Pass on Wednesday
night and early Thursday morning. The current forecast is more
reflective of the first, more probable, solution.

As far as north-central Idaho, west-central Montana, and northwest
Montana are concerned, Thursday and Friday are looking like the
warmest days of the week and ensemble solutions are liking a brief
period of high pressure. Another round of unsettled weather is the
most probable solution for next weekend. However, timing and
amplitude of a low pressure system moving onshore are still very
much in question.


&&

.AVIATION...Showers continue to increase in coverage across
north-central Idaho and western Montana, as seen on satellite and
radar imagery, with isolated thunderstorms also observed. High-
resolution models indicate multiple rounds of showers from this
evening through Monday morning as a trough approaches from the
west and moves into the Northern Rockies. Snow levels are expected
to lower to around 4,500 feet, with terrain becoming obscured in
clouds and snow showers. Periods of reduced visibility, lowered
ceilings, and gusts of 2025 knots are likely in the valleys,
including near TAF sites. Showery conditions and increasing west
winds are expected to persist on Monday as the trough moves
overhead.

&&

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

$$