Elk River, Idaho Weather Forecast Discussion

299
FXUS65 KMSO 201912
AFDMSO
Area Forecast Discussion
National Weather Service Missoula MT
112 PM MDT Sat Sep 20 2025
.DISCUSSION...
KEY MESSAGES:
- Breezy with showers and thunderstorms on Sunday
- Widespread frost possible in valleys by Tuesday morning
A significant pattern change will occur on Sunday as the
ridge of high pressure breaks down and a Pacific cold front
traverses the Northern Rockies. Westerly surface winds will
increase Sunday 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. These winds will
create significant chop on area lakes, including Flathead Lake.
However, latest guidance suggests wind speeds will remain just
below Lake Wind Advisory criteria; this trend will be monitored.
Scattered thunderstorms are forecast to develop along and ahead of
the front during the afternoon 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.
A cooler and drier airmass will filter into the region behind
the front for Sunday night 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.
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 about
5 to 10 degrees above average through the end of the week.
&&
.AVIATION...Aviators should prepare for deteriorating conditions
on Sunday as a Pacific cold front moves through the Northern
Rockies. Expect increasing westerly surface winds with widespread
gusts of 15 to 25 kts, and isolated gusts exceeding 35 kts,
especially near the Continental Divide and in association with
convective activity. Scattered afternoon thunderstorms, mainly
along and south of the I-90 corridor, will bring strong, gusty
outflow winds and brief heavy rain. This will lead to locally
reduced visibility and ceilings and obscured mountainous terrain.
Conditions will improve Sunday night into Monday as a cooler,
drier airmass moves in, with diminishing winds expected for
Monday.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&
$$

NWS MSO Office Area Forecast Discussion