035
FXUS65 KMSO 221001
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
401 AM MDT Tue Apr 22 2025

.DISCUSSION...


KEY MESSAGES:

-  Isolated to scattered showers across western Montana through
   mid week.

-  Gradual warming by the end of the week.

-  Cool and showery conditions this weekend into next week.


The Northern Rockies will continue to be under weak northwesterly
flow aloft today with a few lingering showers impacting western
Montana, especially across the northern portion of the Continental
Divide.

A subtle disturbance will be moving through the Pacific Northwest
on Wednesday which will increase the shower activity across north
central Idaho into southwest Montana. The latest model runs are
showing that this disturbance will transition into a weak cut-off
low pressure system that lingers over central Idaho into Thursday
even though a ridge of high pressure slides over the region.
Temperatures are still anticipated to gradual warm from Wednesday
into Thursday. This cut off low is expected to keep scattered to
numerous showers impacting areas south of the Hwy 12 corridor,
especially on Thursday afternoon.

This lingering low will quickly move off to the east as the upper
level flow transitions to southwesterly by Friday. This flow
pattern will keep the warming trend going over the Northern
Rockies, but this flow pattern is conducive for the development of
showers and thunderstorms by Friday afternoon.

All the models are showing that a broad trough of low pressure
will settle over the western United States by this weekend causing
the Northern Rockies to be under cool and showery conditions. The
extent of the precipitation is still uncertain at this time, as
the exact path of the low pressure system is unknown.

&&

.AVIATION...
Patches of morning valley fog, especially near GPI, will
dissipate shortly after sunrise this morning. Expect visual
weather conditions across the entire region today with pockets of
elevated convection-based snow/rain showers likely after 1900z
under generally light west-northwesterly winds that may gust to
20kt in the vicinity of showers during the afternoon.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...Frost Advisory until 8 AM PDT this morning for
     Orofino/Grangeville Region.

&&

$$