138
FXUS65 KMSO 041914
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
1214 PM MST Wed Dec 4 2024

.DISCUSSION...

KEY MESSAGES:

-  Ridge of high pressure through end of the week causing stable
   conditions with valley fog and stratus

-  Cold front this weekend with wintry mix potential to start, the
   light valley snow accumulations late Sunday into Monday morning

Tuesday`s high clouds have allowed for an expansion of valley
cold pools, as demonstrated by the development of stratus and fog
I-90 west of Missoula and the Missoula and Bitterroot Valleys.
Valley cold pools will continue to strengthen through Friday. The
potential will exist for lowered visibility at times in fog and
patchy black ice.

On Saturday, a weak wave will move into northwest Montana. There
are strong valley inversions and precipitation is expected to
start as a wintry mix. Locations west of US-93 and north of I-90
should plan for scattered icy spots if traveling. Snow levels are
forecast to rise to around 6000 feet, however, mountain passes
such as Lookout and Marias may receive a trace to a couple inches
before changing to rain.

As the Pacific Cold Front approaches Saturday evening west winds
are expected to erode most valley cold pools, places like the
Yaak, Olney, and Polebridge may not completely erode and icing
issues could continue. All other valley locations will experience
a period of downsloping, receiving as little as 1/3 to 1/4 the
total precipitation of nearby mountains.

Sunday snow levels crash back into the valleys and widespread
there is a 40-50% chance of receiving at least a trace of snow,
while only high elevation valleys in Idaho County have a high
probability of receiving greater than an inch. Impacts to travel
will be possible at Mountain passes such as Lookout, Lolo, Marias,
and Lost Trail where 3 to 7 inches is the 25th to 75th percentile
snow total.

Monday northerly flow develops ushering in cold Canadian air.
Northerly flow is a good regime for snow in the Camas Prairie ID,
especially Grangeville. The current forecast only shows very
light snow, please keep checking future forecast evolutions. The
temperature forecast for this period is warmer than would be
expected for this scenario, likely due to modeled cloud cover.
Locations that see clearing Tuesday morning could see low
temperatures in the single digits, to potentially near zero in
western Montana and Lemhi County, ID.




&&

.AVIATION...Stable conditions continue the next several days under
a ridge of high pressure. Fog and low stratus has been present
across many valleys of north central Idaho and across northwest
Montana. The fog and stratus will likely erode somewhat each
afternoon then increase in coverage and thickness each night. Fog coverage
has expanded into the Missoula Valley, lowered visibility and low
ceilings can be expected into the afternoon through Friday. The
remainder of the region will have increasing potential for
visibility reductions from localized fog each morning through
Friday.

&&

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

$$