Butte, Montana Weather Forecast Discussion

678
FXUS65 KMSO 021850
AFDMSO
Area Forecast Discussion
National Weather Service Missoula MT
1250 PM MDT Thu Oct 2 2025
.DISCUSSION...
KEY MESSAGES:
-  Scattered showers and isolated thunderstorms today turning to
   steady rain overnight for some.
-  A significantly colder trough on track for late Saturday into
   Sunday with snow levels lowering. Significant mountain snow
   possible.
-  Widespread frost/freeze for Monday and tuesday mornings.
The cool, unsettled pattern continues today under the influence
of a broad upper-level trough and moist southwest flow. As during
the past few days, diurnal heating will once again trigger
scattered showers and isolated thunderstorms this afternoon. The
overall wind field has relaxed slightly compared to Wednesday, but
breezy conditions will still be felt especially over ridges and
near any thunderstorms or stronger showers that develop today.
Overnight steady light-to-moderate rainfall is likely from Idaho
and Lemhi counties north and eastward into the Bitterroot,
Missoula, and Seeley/Swan valleys. There is a very isolated risk
for excessive rainfall intensities in the southern Bitterroot.
Some light snow showers and accumulation is possible above 9000
feet in this area.
Confidence continues to grow in the weekend forecast and model
guidance has solidified on a track of the broad trough,
attempting to close off, and mid-level low that favors more
widespread and persistent precipitation developing across the
region Saturday into Saturday night. Snow levels will slowly start
do descend to near 7000 feet through the day.
The primary forecast challenge and greatest potential impact
arrives Saturday night into Sunday. Model consensus is now quite
firm that a secondary, much colder trough will dive south out of
Canada and merge with the cutoff low. This will pull a
significantly colder airmass into the region, causing snow levels
to fall to around 5000 feet by Sunday morning. Probabilistic
guidance has trended upward significantly and now shows an 80%
chance for at least 2 inches of snow and a 50% chance of at least
6 inches of snow by Sunday afternoon for elevations above 7000
feet along the Continental Divide including Glacier National Park.
As such, a Winter Storm Watch has been issued for this time frame
as backcountry travelers and interests at high elevations should
begin preparing for the first significant mountain snow event of
the season. In general, people in most mountain locations above
6000 feet should prepare for winter-like conditions including in
the Bitterroot, Sapphire, Anaconda-Pintler, Flint Creek, Swan,
Mission, and Rattlesnake Ranges.
Cold temperatures and clear skies to follow on Monday and Tuesday
mornings with most locations, aside from far western areas of
north-central Idaho, forecast to be in the 20s and 30s. Care
should be given to sensitive outdoor vegetation and preparations
should be made to begin winterizing things such as homes,
properties, and vehicles for the upcoming winter season.
&&
.AVIATION...Scattered showers and isolated thunderstorms possible
again this afternoon and evening. Steady light-to-moderate rain
will mainly impact KSMN, KHRF, KMSO, and the Seeley Lake region
between 03/0400z and 03/1800z. Low stratus and isolated areas of
fog are likely to develop overnight and through Friday morning in
this region.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch from late Saturday night through Sunday
     morning for West Glacier Region.
ID...None.
&&
$$

NWS MSO Office Area Forecast Discussion