383 
FXUS65 KMSO 041151
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
451 AM MST Wed Dec 4 2019

.DISCUSSION...

Moisture will continue to stream across northwest Montana through
at least Thursday, as a ridge of high pressure amplifies along 
the Pacific Northwest coast. Periods of very light, very brief 
precipitation are anticipated during this time. Most low 
elevations will observe only light rain (sprinkles). There are 
still a few narrow valleys that are still receptive to freezing 
rain on roadways, including the Highway 200 corridor west of 
Thompson Falls to the Idaho border and Highway 93 between Eureka 
and Whitefish. Similar to Tuesday, there will be high variability 
in the presence of ice on roadways across northwest Montana 
through today. Temperatures will be be quite mild for the much of 
the region today, with most locations warming near or above the 
seasonal average. Despite the warmer temperatures, the high 
moisture content in the air will be conducive for fog and freezing
fog across northwest Montana tonight through Thursday morning.

Conditions will gradually dry across the Northern Rockies 
Thursday to Friday, as warm high pressure moves overhead from west
to east. Temperatures will remain quite mild during this time, 
particularly for the lowest elevations of north central Idaho, the
southern Bitterroot Valley, the southern Mission Valley, and near
Eureka. Fog will continue to be a threat for northwest Montana 
valleys again Thursday night through Friday morning.

A Pacific storm system and a relatively cold continental storm 
system from east of the Continental Divide will interact over the
Northern Rockies this weekend. First, the Pacific influenced storm
system will produce widespread rain/snow mix for low elevations on
Saturday. Modest snow accumulations are expected to be confined
near area mountain passes on Saturday. Next, a blast of arctic air
will move westward over the Continental Divide on Sunday,
producing gusty east and northeast winds across western Montana.
It appears that the meeting point of the Pacific and arctic
airmasses (i.e., the Continental Divide of northwest Montana) is
also where the most significant snow accumulation will occur.
There is reasonably high likelihood for more than 1 foot of snow
accumulation in the Glacier Park region from this meeting of
airmasses, however it is unclear how this interaction will
translate to low elevation snow in the nearby Flathead Valley or
the rest of the Northern Rockies. Even in the absence of
significant snowfall, gusty winds and wind chill down to near zero
will have an impact on area travel and safety.

The arctic cold air will become trapped in the valleys of the Northern
Rockies early next week, as high pressure moves overhead. Valley
temperatures inversions, low stratus, and patchy freezing fog will
become common by Tuesday.

A snowy pattern may loom beginning the middle of next week for the
Northern Rockies, however not all models currently agree with a 
prolonged wet spell.

&&

.AVIATION...Moist westerly flow keeps low stratus decks over KGPI
and KMSO for the next 24 hours. KGPI could also see some light
rain and snow through about 05/0600Z tonight. Precipitation will
be more intense and obscure terrain over the mountains of
northwest Montana. 

&&

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

$$