Damaging Wind in Idaho, June 19, 2025

Area Forecast Discussion
National Weather Service Missoula MT
133 PM MDT Thu Jun 19 2025

.DISCUSSION...

KEY MESSAGES:

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

- Widespread precipitation Friday afternoon through the weekend.
  Much cooler temps, high elevation snow.

- Significant snowfall, for this time of year, across Glacier
  National Park and the Flathead National Forest Saturday into
  Sunday morning.

Mid-level moisture is increasing subtly this afternoon under
southwesterly flow. Surface dewpoint depressions will contribute
to high-based storms with gusty outflow potential. The greatest
amount of surface-based CAPE will remain south of I-90. Like many
previous thunderstorms events in the past couple weeks. The
highest threat for strong-to-severe wind gusts from these storms
will be across southern Ravalli, Granite, Deer Lodge, Silver Bow,
and Lemhi counties this afternoon.

As a seasonably-cold pacific low continues to push onshore over
the next couple days, moisture availability will only continue to
increase. Friday will provide numerous opportunities across a
widespread area for convectively-forced showers and thunderstorms
starting early in the morning and lasting through much of the day.
The most widespread and heaviest precipitation will be found
within the northern half of the anticipated incoming closed low
across Lincoln and Flathead counties especially later in the
evening and overnight into Saturday.

Convective showers on Friday will then turn increasingly
synoptically forced with more of a widespread light-to-moderate
rainfall and high elevation snow through the day Saturday and
periods of dryer conditions during the afternoon across
southwestern and west-central Montana.

There is the potential for significant accumulating heavy and wet
snow (up to a foot or more) above 5,000ft within Glacier National
Park and surrounding national forest lands. Snow levels may
briefly drop and bring a couple flakes as low as 4,000ft late
Saturday night and early Sunday morning with the heaviest snowfall
and coldest temperatures forecast during this time frame.
Anticipate the potential for rapidly changing conditions in valley
locations near Glacier and along US-2. The risk for snow, cold &
blustery winds, and resulting reduced visibility raises concerns
for any backcountry users and high-elevation destination-seekers
(especially tourists whom aren't accustomed to the near-winter
conditions frequently found in the Montana high country). For
this reason, a Winter Storm Watch will remain in effect leaving
the decision to upgrade to an Advisory or Warning to successive
shifts for now.

Elsewhere, widespread valley rain and mountain snow (above
6,000ft) will likely continue for Flathead and Lincoln counties,
while spotty valley rain and mountain snow showers continue under
northwest flow across the rest of the Northern Rockies Saturday
and into Sunday. Recent model trends have continued to increase
precipitation totals across most of the area with a 9/10 chance
for widespread totals over 0.25" of precipitation and about a 50%
chance to see near or over 1.5" north and northeast of the
Flathead Lake area over a 48-hour period ending Sunday evening.

Forecast highs on Saturday and Sunday will be cold for this time
of year (within 2 degrees of a daily record for Saturday, June
21st's coldest maximum temperature in Missoula specifically) in
the mid-upper 50s.

As the low moves east of the region heading into Monday,
progressive drying conditions will settle in overhead but
temperatures will remain cold. Dependent on cloud cover, Monday
morning lows are anticipated to be in the 30s for most with the
risk of dropping to near and below freezing at many higher
elevation valley locations. Though drier than the previous couple
days, chances still remain for spotty showers and storms
especially during Monday afternoon. Continued drying with much
more seasonable weather to follow into next week.

&&

.AVIATION...Scattered showers and thunderstorms will develop
across Lemhi County, ID and southwest Montana, this afternoon,
with convective initiation beginning by 19/2100Z. Storms will
track quickly to the northeast, with the highest threat of
lightning (50-60% chance) across Silver Bow, Deer Lodge, and
Powell Counties between 19/23Z-20/0300Z. Strong thunderstorms are
expected across these areas, with an isolated threat (5%
probability) for severe damaging winds of 50kts. Deepening south-
southwest flow ahead of a closed low will bring increased moisture
and instability overnight into Friday morning, with convection
moving south to north across central ID starting around 20/0600Z,
before spreading into west-central and northwest Montana through
20/08Z and 20/12Z respectively.

&&

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

ID...None.
&&