Wind Advisory 3, NWS Missoula, MT

Area Forecast Discussion
National Weather Service Missoula MT
304 AM MDT Fri Mar 21 2025

.DISCUSSION...

- Continuing light showers across northwest / west-central
  Montana, and northern Idaho through this morning.

- Vigorous Pacific cold front Friday afternoon into Saturday
  morning, with moderate to heavy mountain snow.

- High confidence in a period of above-normal temperatures
  beginning Tuesday, March 25.

Satellite imagery this morning displays a longwave trough moving
into the Pacific Northwest with the northern Rockies situated underneath
the exit region of this upper level jet stream which has increased
synoptic scale lift across the region. The first surge of
moisture associated with this system has been producing scattered
light mountain snow and valley rain/snow showers, portrayed by
radar and webcams, which will continue through the day on Friday
with snow levels steadily rising into the afternoon.

Snow levels will then lower rapidly from above 4000 feet down to
valley floors late Friday night into early Saturday morning. One
of the main concerns with this storm are the convective snow
bands forecast to form along and just behind the cold front.
There is significant agreement in timing and intensity among
recent runs of convective allowing models (CAMs) to suggest a
brief period (1-3 hours) of snowfall rates approaching one inch
per hour during the frontal passage. Valley areas may see a quick
half an inch of snow during this period as the front passes Friday
night into Saturday morning. Mountainous terrain will
additionally experience blowing snow and gusty winds through
Saturday.

Showers becomes less of a concern in lower elevations and valleys
by Sunday. However, an enhanced plume of Vertically Integrated
Water Vapor Transport (IVT) riding over the top of a building
upper-level ridge moves onshore and pushes more moisture into the
region on Monday. This plume is likely to couple with an upper-
level shortwave trough that refocuses light to moderate
precipitation across western Montana and north central Idaho.
Anticipate additional snow impacts to mountain passes and periodic
showers in valleys. Precipitation will finally diminish Tuesday
as the upper level ridge builds in overhead and high pressure
strengthens.

Confidence remains high (greater than 80%) for daytime high
temperatures to climb into the 70s through Wednesday in central
Idaho valleys, and into the upper 60s for western Montana valleys.
High temps eclipsing the 70 degree mark for the first time this
spring is still not out of the question for western Montana. The
valleys with the best chance (10-20% probability) of reaching 70
degrees next Wednesday, March 26, will be the Bitterroot and
Missoula valleys. Lesser chances (<10% probability) exist from
Drummond to Anaconda.

&&

.AVIATION...
Scattered showers moving within southwesterly flow are
evident in regional radar imagery this morning, with activity
focusing along the ID/MT border and in northwest Montana. This
will continue to be the trend through 21/1800z, leading to terrain
obscurations, with snow levels rising to 4,000-4,500 feet heading
into the afternoon. South-southwest winds will increase between
21/1600-1800z, with frequent gusts of 20-30kts as the gradient
tightens as a cold front pushes into eastern Washington.
Widespread precipitation will move into the ID/MT border by
22/00z. High resolution models are in strong agreement for a
convective band of precipitation to develop along the front,
leading to temporary visibility reductions across western Montana
from 22/0000-09000z. Furthermore, strong winds over mountain
crests will lead to widespread mountain wave induced turbulence
through 22/09z.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory from 6 PM this evening to noon MDT
     Saturday for Bitterroot/Sapphire Mountains...West Glacier
     Region.

     Winter Storm Warning from 6 PM this evening to noon MDT Saturday
     for Lower Clark Fork Region.

     Winter Weather Advisory from midnight tonight to noon MDT
     Saturday for Butte/Blackfoot Region...Potomac/Seeley Lake
     Region.

ID...Winter Weather Advisory from 6 PM MDT /5 PM PDT/ this evening to
     noon MDT /11 AM PDT/ Saturday for Eastern Lemhi County...
     Northern Clearwater Mountains...Southern Clearwater
     Mountains.

&&