515
FXUS65 KMSO 261939
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
139 PM MDT Sat Apr 26 2025

.DISCUSSION...

KEY MESSAGES:

-  Showers and thunderstorms through this evening and again
   Sunday, with isolated outflow winds up to 40 mph.

-  North-northeast wind shift, with gusts of 25-35 mph along the
   divide, with choppy lake conditions Sunday evening.

-  Cooler and wetter pattern anticipated late Sunday into Monday.
   Snow accumulations above 5,500 feet across Lemhi County and
   along the Continental Divide.

Satellite imagery this afternoon shows a mid-level circulation
over the northern Bitterroot Mountains, with numerous showers and
isolated thunderstorms developing in the warm sector to the south
and east. Forecast soundings suggest modest instability through
this evening across north-central Idaho and west-central Montana,
with dry lower levels of the atmosphere creating an ideal set up
for areas of outflow winds of 30-40 mph. Showers and thunderstorm
life cycles will be short lived given a lack of vertical wind
shear, therefore outflow boundaries will tend to be more
localized in nature, with longer lived outflow boundaries in
north- south oriented valleys, such as the Bitterroot.

A closed low over CA/NV will move northeastward Sunday into
Monday, with moisture increasing tonight into Sunday morning.
Therefore, another round of shower and storm activity is expected
Sunday, with outflow winds of 30-40 mph, brief heavy rain, and
lightning being the primary storm threats. The closed low will
stall into southeast Idaho Sunday evening into Monday morning,
with a cold front dropping southward from Canada. A north-
northeast wind shift is expected as the front arrives across
northwest Montana and along the divide Sunday evening. This wind
shift will bring choppy conditions to area lakes, including
Flathead Lake, Georgetown Lake, and bodies of water in the
Seeley-Swan Valley.

Precipitation will focus across Lemhi County into southwest
Montana Sunday into Monday morning, where a north-northeast
gradient will bring the highest precipitation totals along the
divide. Precipitation amounts will range from 0.10-0.30 inches in
the valleys, with 0.50-1.00 inches in the higher terrain.
Snow will focus above 5,500 feet, with minor slushy accumulations
across MacDonald, Homestake, Lost Trail, and Bannock Passes.
Remote mountain areas above 6,500 feet in Lemhi County will see
the highest snow amounts, with six inches or more of snowfall.

By Tuesday and Wednesday next week, model guidance suggests
another trough of low pressure will move through the area from the
northwest. Breezy west-northwest winds will develop along with
scattered shower activity. A warming trend is anticipated by
Thursday into Friday, with ensemble models pointing towards high
confidence (>90% chance) for a broad ridge of high pressure.


&&

.AVIATION...Showers and isolated thunderstorms will become more
numerous through the afternoon and early evening, then decreasing
in coverage significantly after 27/0300z. KMSO, KHRF, KBTM and
KSMN have the best chances (30 to 50 percent) of seeing a brief
shower or thunderstorm, while KGPI has a limited threat (20
percent). In addition to lightning, storms will be capable of
erratic wind gusts up to 35 kts locally.

&&

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

$$