623
FXUS65 KMSO 011902
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
102 PM MDT Thu Oct 1 2026

.DISCUSSION...

KEY MESSAGES:

-  Warming and drying trend Friday through Sunday; cool/cold
   valley lows with patchy frost.

-  Westerly winds increase Friday afternoon and Monday with
   passing disturbances.

Zonal flow aloft will yield to a building high-pressure ridge
across the Northern Rockies Friday through Saturday. This will
initiate a warming and drying trend, with daytime high
temperatures rising roughly 10 to 15 degrees (or more) above
seasonal averages this weekend. Strong nocturnal radiational
cooling under clear skies will allow valley temperatures to drop
into the 30s overnight, producing patchy frost in cold-prone
locations. Isolated, shallow morning valley fog is possible in
low-lying basins, though widespread impacts are unlikely.

A weak upper-level shortwave tracking along the Canadian border
Friday afternoon into Friday night will temporarily tighten
pressure gradients, increasing westerly surface wind gusts to 20
to 25 mph across Northwest Montana and higher terrain.

Upper-level high pressure will maintain dry, warm conditions on
Sunday. A second weak disturbance will slide east through the
region Monday into Tuesday, flattening the ridge and bringing an
uptick in westerly winds. Some destabilization associated with
this feature may support isolated afternoon showers and deeper
mixing. High pressure will rebuild mid-to-late next week,
maintaining dry and warm conditions. Long-range ensemble guidance
shows a low probability (40%) of an upper-level change knocking
down the ridge around October 9th to 10th, though confidence
remains low this far out.

&&

.AVIATION...Widespread VFR conditions will prevail across the
Northern Rockies airspace through Friday morning under passing
mid- and high-level clouds. Clear skies and light surface winds
tonight will promote strong radiational cooling, leading to
isolated morning valley fog in fog-prone basins between 02/1000Z
and 02/1500Z, though terminal impacts will remain minimal. A weak
shortwave disturbance tracking along the Canadian border Friday
afternoon will increase westerly surface winds to 15 to 20 knots
at all terminals through Friday evening, generating localized low-
level turbulence near ridge crests.


&&

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

$$