843
FXUS65 KMSO 211933
AFDMSO
Area Forecast Discussion
National Weather Service Missoula MT
133 PM MDT Sat Jun 21 2025
.DISCUSSION...
KEY MESSAGES:
- Widespread precipitation through Sunday
- Accumulating mountain snow above 5,000-6,000ft for Glacier N.P.
and Flathead National Forest. Increased risk of hypothermia for
backcountry users.
- Frost potential Sunday and Monday mornings western Montana
valleys
Theres no time like the first day of summer to talk about snow
in the Northern Rockies. Satellite imagery this afternoon is
depicting a closed midlevel low pressure circulation centered over
central Idaho. A secondary low is setup just east of the
Continental Divide on the Canadian border. A deformation band
north of the secondary low pressure center is sitting over
southern Alberta. The deformation band will shift southward over
northwest Montana later this afternoon and overnight tonight as
both low pressure centers move east. This feature will enhance
precipitation over northwest Montana through Sunday morning,
especially over the Glacier Park area and the northern portions of
Flathead and Lincoln counties. Heavy, wet snow remains likely
above 5,000 feet, with localized totals exceeding about a foot in
the more remote locations of Glacier Park. Snow levels may briefly
dip to around 4,000 feet tonight into early Sunday morning during
the coldest period of the system, coinciding with the heaviest
snowfall. These conditions may lead to rapidly deteriorating
travel, especially around Glacier NP. In addition to the snow,
cold temperatures and gusty winds could significantly reduce
visibility and create hazardous conditions for backcountry users
and high- elevation visitors, especially those unprepared for
winter-like weather. Twenty-four hour liquid precipitation amounts
ending around midday on Sunday will be a widespread 0.25 to 0.5
inches for most of the Northern Rockies, with 0.5 to 1.5 inches
for northern Lincoln/Flathead counties including Eureka, Glacier
Park, and the northern Swan/Flathead ranges.
The focus for precipitation will shift to southwest Montana and
Lemhi County on Sunday afternoon as the larger scale low clears
the Continental Divide. Wraparound moisture will result in
continued rainfall for areas just west of the Divide. Snow levels
will be around 6000 feet, so backcountry travelers should be
prepared for a more winter-like experience than what one would
expect for the second day of summer.
Temperatures today and Sunday will be unseasonably cold. Daytime
high temperatures will be about 10-15 degrees below normal.
Overnight lows will also be on the cool side, with cloud cover
dampening some potential for further cooling. Nonetheless, if you
have plants that are sensitive to frost, please check the
numerical forecast for the low temperatures in your location for
Sunday and Monday mornings. The higher valleys of western Montana
and north-central Idaho will be down to the low to mid 30s with
chances of upper 20s in places like Seeley Lake, Georgetown Lake,
Ovando, and Butte. Expect a return to near normal daytime high
temperatures on Monday as upper level flow becomes mostly westerly
behind this weekends disturbances. A shift to southwesterly flow
later in the week will bring some chances for afternoon
thunderstorms on Thursday and Friday for southwest Montana and
Lemhi County.
&&
.AVIATION...A deep cut-off low remains over the region today
causing mid level ceilings and rain showers. Snow levels will drop
down to around 5,000 to 6,000 ft elevation tonight, though no
accumulating snow is expected at any area major terminals from
this system. Some high elevation back country air strips in
central Idaho and western Montana may be affected by accumulating
snow, but it`s also likely that these air strips will also be
unusable due to low ceilings and poor visibility. Showers and mid-
level ceilings will continue to affect major terminals through
Monday as the upper level low slowly meanders out of the region.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory until noon MDT Sunday for
Bitterroot/Sapphire Mountains...Butte/Blackfoot Region...
Potomac/Seeley Lake Region.
Winter Storm Warning until noon MDT Sunday for West Glacier
Region.
ID...Winter Weather Advisory until noon MDT /11 AM PDT/ Sunday for
Eastern Lemhi County...Southern Clearwater Mountains...
Western Lemhi County.
&&
$$
