859
FXUS65 KMSO 261949
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
1249 PM MST Tue Nov 26 2024

.DISCUSSION...

KEY MESSAGES:

-  A shortwave today will bring some light snow across the region
   with minimal impacts

- Growing confidence that a strong ridge of high pressure will
  develop bringing a period of air stagnation and potential valley
  fog and stratus.

Continued snow shower activity today, mainly south and west of
Missoula and ending by early evening. Currently, any impacts will
be limited to brief periods of time at mountain passes within
Lemhi County, such as Lost Trail, Gilmore Summit, Lemhi, and
Bannock.


Wednesday will bring a short lull in shower activity but cloud
cover will remain for most. A minority of the models continue to
demonstrate the possibility for a couple of weak waves moving
through northwest flow Thanksgiving Day through Saturday. While
the potential for a few periods of light snow exists, no single
event stands out with the ability to bring widespread impacts. As
always during the winter season, prepare for slick spots on
bridges or shaded roadways if traveling.

Forecasts evolve overtime, yesterday the scenario Saturday onward
was lower probability for a dominant ridge to develop. Today
confidence is increasing for the dominant ridge to not only
develop but sustain through at least the first week of December.
Please read our `Air Stagnation` section for more details. After
Saturday expectations are increasing for degrading air quality
and for days to start off with fog or low stratus clouds in
valleys. There are some wild cards in this particular scenario
that will only resolve themselves in the short term.


&&

.AVIATION...A trough moving through from the northwest today will
cause light snow showers to continue with only minor accumulations
expected, and even then mainly in the mountains. Impacts at
terminals will mainly be low to mid level ceilings and
intermittent visibility restrictions due to light snow or mist.
Shower activity is expected to decrease from northwest to
southeast after 26/2100z. High pressure develops Wednesday, the
potential for fog and low ceilings will be present at KGPI, KMSO,
KGIC, KHRF, and KSMN through noon.


&&

.AIR STAGNATION...Confidence is increasing for a dominant, strong
ridge of high pressure to exert its influence as early as Thursday
but with higher confidence by Saturday. Two key components will
be lacking for many valleys, cold air and snow cover, so
development could be gradual. Our concerns center on the
longevity of the event potentially lasting beyond the 1st week of
December. Expect after Saturday, stable conditions allowing for very
poor valley ventilation.




&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...Winter Weather Advisory until 8 PM MST this evening for Eastern
     Lemhi County.

&&

$$