932
FXUS65 KMSO 121956
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
156 PM MDT Sat Jul 12 2025

.DISCUSSION...

KEY MESSAGES:

-  Warming trend with the weather pattern during weekend, with
   moderate heat risk impacts across low elevations of north-
   central Idaho.

- A big change is likely (>90%) across the region later Monday
  into Tuesday with much cooler and wetter conditions across the
  region, especially along the Divide, and Glacier National Park.

- Strong northeast winds 30-40+ mph Monday and Monday night
  possible in channeled areas could trigger spotty power outages,
  and tree limb damage.

High temperatures will climb into the low-100s for lower
elevations of north-central Idaho this weekend, where heat
advisories remain in effect for the Lower Hells Canyon/Salmon
River Region and Orofino and Camas Prairie Regions. Consider
practicing heat safety by drinking plenty of fluids, and resting
in shaded or air conditioned environments when working outside.
Hot and dry weather, along with breezy westerly winds, each
afternoon, will lead to elevated fire weather conditions.

There is high confidence for a brief pattern change Monday through
Wednesday as a relatively rare low pressure system digs south out
of British Columbia. We spent a little bit of time looking for
similar/matching patterns since the 1950s. We didn`t find any
exact matches, but there were a few cases that came close. There
were a lot of troughs that tracked west to east from the Pacific
Coast, but hard to find cases where a trough dove southeast out
of BC with a very large upper ridge over the northeast Pacific.
There was a case, August 15-16, 1985 that had some similarities
including a fast moving BC trough sliding southeastwards into the
Northern Rockies. That event brought 0.50 to 1.00" of rainfall to
the Glacier Region, and some of the amounts were higher east of
the Divide. Our present case digs a LOT more to the south. The
reason for this is because of the strong upper ridge upstream.
This bodes well for possible heavy precipitation totals across
northwest Montana. The higher percentiles suggest that
precipitation totals over 1.00" are possible (10-20% chance) in
the higher terrain from east of Libby, eastwards to Glacier
National Park. Ensembles and machine learning model ensembles seem
to be forming a consensus of the trough positioned over eastern
Washington State and the northern Idaho Panhandle Tuesday morning.

The backcountry could feel very winter-like for many out-of-state
visitors to the region. The combination of temperatures in the
30s and 40s, steady rainfall, gusty easterly winds of 20 to 50
mph, and fog could be dangerous for those caught off-guard! The
peak of the winds and heavier precipitation rates seems to occur
Monday evening through Tuesday.

Due to the fact that there will be 1008 mb low pressure over
north-central Idaho on Monday evening, this will help to draw the
colder air southwards. Along and behind the cold front passage,
there could be strong northeast winds ranging between 25 and 50
mph. This could trigger spotty power outages, tree limb damage,
and pose a significant risk to those recreating on area lakes like
Flathead Lake.

Snow levels will range between 8,000 and 10,000 feet MSL across
northwest Montana. Heavier precipitation rates Monday night into
Tuesday morning could drive the snow down to 7,000 feet in Glacier
National Park. There could be several inches of snow on the
mountain peaks on Tuesday.


&&

.AVIATION...Gusts of 15-20 kts will continue to develop across
the region, including most TAF sites. The higher gusts will focus
across northwest Montana and along the divide through this
afternoon and evening. Winds relax this evening before returning
for Sunday afternoon. Hot temperatures also return on Sunday.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...Heat Advisory until 8 PM PDT Monday for Lower Hells
     Canyon/Salmon River Region...Orofino/Grangeville Region.

&&

$$