Ravalli, Montana Weather Forecast Discussion

877
FXUS65 KMSO 210744
AFDMSO
Area Forecast Discussion
National Weather Service Missoula MT
144 AM MDT Sun Sep 21 2025
.DISCUSSION...
KEY MESSAGES:
- Breezy with showers and thunderstorms on today.
- Widespread frost possible (greater than 50%) in western Montana
  valleys by Tuesday morning.
A significant pattern change is on track for today as a ridge of
high pressure breaks down and a Pacific cold front traverses the
Northern Rockies. Westerly surface winds will increase this
afternoon, with widespread gusts of 20 to 30 mph expected.
Isolated stronger gusts, potentially exceeding 40 mph, are
possible, particularly along the Continental Divide and in
association with any convective downdrafts. Gusty conditions are
expected between 2 PM and midnight tonight. These winds will
create a noticeable increase in chop on area lakes, especially
Flathead Lake where wave heights of 1 to 2 feet are expected
along the northernmost half of the lake. However, the latest
guidance suggests wind speeds will remain just below Lake Wind
Advisory criteria, though this trend will be monitored.
Scattered thunderstorms are forecast to develop along and ahead of
the front during the afternoon and evening hours, especially along
and south of the Interstate 90 corridor, including Lemhi County
and southwest Montana. The primary threats with any storms will be
strong, gusty outflow winds and brief heavy rain, with the best
timing from 2 PM to 8 PM this evening.
A cooler and drier airmass will filter into the region behind the
front for tonight and Monday. With clearing skies and diminishing
winds Monday night, conditions will become favorable for the first
widespread valley frost of the season by Tuesday morning.
Sheltered, low-lying areas across western Montana and the higher
valleys of north-central Idaho have the highest potential for
seeing temperatures drop to near or below freezing. The
probability for frost is highest (90 percent) in the Deerlodge,
Butte, and Anaconda areas, with lower probabilities (50 percent)
for the valleys along Highway 93.
A transient upper ridge is forecast to rebuild over the area for
Tuesday and Wednesday, resulting in a moderating temperature
trend. The combination of clear nights, light winds, and residual
low-level moisture will support the potential for patchy river
valley fog each morning. By Thursday and Friday, models show the
ridge shifting eastward as an upper trough approaches from the
Pacific. This will re-establish southwesterly flow aloft,
increasing moisture and instability for a renewed chance of
afternoon showers and thunderstorms. Temperatures are expected to
remain more than 10 degrees above average through the end of the
week.
&&
.AVIATION...VFR conditions this morning will deteriorate this
afternoon and evening as a Pacific cold front brings gusty winds
and thunderstorms to western Montana and north-central Idaho.
After 20Z, expect westerly surface wind gusts of 20-25 kts for
all terminals. Scattered thunderstorms are also forecast between
20Z Sunday and 02Z Monday, mainly south of the I-90 corridor
(impacting terminals like KBTM and KSMN). Primary threats will be
strong, erratic outflow winds and temporary MVFR/IFR conditions in
heavy rain. Conditions will improve after 06Z Monday as skies
clear and winds diminish, with VFR returning to all terminals.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&
$$

NWS MSO Office Area Forecast Discussion