640
FXUS65 KMSO 181841
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
1241 PM MDT Wed Jun 18 2025

.DISCUSSION...


KEY MESSAGES:

- Warm, dry and breezy conditions Thursday.

- Strong thunderstorms, with isolated severe threat, Thursday
  into Friday across west-central and southwest Montana.

- Widespread precipitation Friday night into the weekend, with
  cooler temperatures, and high elevation snow.

A weak ridge of high pressure will remain across the Northern
Rockies through today, with above-normal temperatures, and plentiful
sunshine. Deep atmospheric mixing will lead to breezy winds this
afternoon, with gusts of 15-25 mph in the valleys and 25-35 mph
across the higher terrain.

Showers and thunderstorms will return Thursday across southwest
Montana, focusing across Ravalli, Granite, Deer Lodge, and Silver
Bow Counties and in Lemhi County, ID as southwesterly flow
transports Pacific moisture and instability into the region.
Forecast soundings suggest inverted-V profiles, along with modest
shear and instability, supporting the development of strong to
isolated severe thunderstorms (5% probability), with strong
outflow winds being the primary concern.

The risk for strong to isolated severe thunderstorms expands into
west-central Montana and along the divide in northwest Montana
Friday. A cut-off low will move inland across the Pacific
Northwest, with south-southwest flow bringing increased moisture
and instability, while the low provides synoptic ascent. Forecast
models suggest isolated thunderstorms will form early in the
morning, with storm coverage expanding by the early afternoon,
spreading south to north from Lemhi County, Idaho and southwest
Montana into west-central Montana and along the divide in
northwest Montana. The environment will support storms capable of
producing small hail, gusty winds, and periods of heavy rain. An
isolated storm or two will be capable of producing large hail and
strong to potentially damaging winds, with the greatest threat
focused along the divide in southwest Montana, north of where a
surface low will deepen in the afternoon. One caveat, will be the
morning activity and residual cloud-cover into the afternoon. This
could help suppress the strongest convection from really getting
going. Stay tuned!

The aforementioned closed low will move eastward across the
Northern Rockies late Friday into the weekend, with widespread
precipitation, cooler temperatures, and high elevation snow
impacting the region. Guidance has trended the low`s track
further south over the last 24-hrs. This trend has lead to higher
precipitation amounts in the forecast, with probabilities for
>0.50 inches of rain increasing above 95% north of I-90, with
50-70% south of I-90. Flathead and Lincoln Counties are favored
to receive the highest precipitation amounts with a 60% chance
for 2 or more inches of precipitation along and north of Highway
2. The result will be the potential for rock and debris slides
along steep terrain in Glacier National Park and Forest Service
roads in the Flathead and Kootenai National Forests. Low land
ponding of water will be possible in poor drainage areas.

Those with plans in the backcountry and/or high elevations should
begin preparing for cold temperatures, accumulating snow, and raw
conditions, including Glacier National Park. Speaking of Glacier
Park, snow amounts have trended higher, with models indicating
4-15 inches of snow, pending on elevation. Of particular note is
Logan Pass, where there middle of the road forecast, is 7 inches
and a 30% probability for up to 10 inches. Due to the late season
snow potential and activity in the backcountry, a Winter Storm
Watch has been issued that goes into effect Saturday. The heaviest
snow is anticipated to fall Saturday evening through early Sunday
morning. Plan accordingly if traveling across northwest Montana,
particularly the higher terrain.

After the low exits the region late Sunday, a cold dry air mass
will settle in behind it. Monday morning low temperatures will
likely be at or below freezing for the higher valleys along the
Continental Divide and mid 30s for the larger valleys along the
Highway 93 corridor.

&&

.AVIATION...VFR conditions will continue today, with plenty of
sunshine and gusty winds this afternoon. Shower and thunderstorm
activity returns Thursday across southwest Montana and Lemhi
County, ID.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch from Saturday afternoon through Sunday
     morning for West Glacier Region.

ID...None.
&&

$$