197
FXUS65 KMSO 180901
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
301 AM MDT Wed Jun 18 2025

.DISCUSSION...

KEY MESSAGES:

- Warm, dry and breezy conditions today.

- 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.

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 lows track further
south over the last 24-hrs, with ensemble means placing the mid-
level circulation moreso along the USA-Canada border, while
previous runs moved the low into southern Alberta. This trend has
lead to higher precipitation amounts in the forecast, with
probabilities for >0.50 inches of rain increasing above 80% north
of I-90, with 40-60% south of I-90. Flathead and Lincoln Counties
are favored to receive the highest precipitation amounts with a
70 and 50% chance for an inch or more of precipitation,
respectively.

Those with plans in the backcountry and/or high elevations should
begin preparing for cold temperatures, accumulating snow, and raw
conditions, including Glacier Park. Speaking of Glacier Park, snow
amounts have trended higher, with models indicating 3-12 inches of
snow, with the highest accumulations above 7,000 feet. Of
particular note is Logan Pass, where there`s a 50% chance for 4
inches or more and a 15% chance of a foot or more.

The low will begin to exit the area Sunday, with scattered showers
continuing with a northwesterly flow pattern.

&&

.AVIATION...VFR conditions will continue today, with plenty of
sunshine. Deep mixing will promote gusty winds after 18/1900Z,
with 20-25kt gusts. Shower and thunderstorm activity returns
Thursday across southwest Montana and Lemhi County, ID.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

$$