136
FXUS65 KMSO 150907
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
207 AM MST Fri Nov 15 2024

.DISCUSSION...

KEY MESSAGES:

-  Light to moderate snow late this afternoon into early Saturday
   for north- central Idaho into southwest Montana.

-  Strong cold front Sunday into Monday bringing hefty snow and
   gusty winds to the higher terrain and potential for snow in the
   valleys. Icy road potential Monday morning.

-  Ridge of high pressure latter part of next week but questions
   of position and strength.

As partial clearing occurs, fog and low stratus are a concern
through late morning in areas that experienced precipitation
yesterday.

A mid-level circulation is still expected over the Snake River
Plain this afternoon, shifting into southeast Montana by Saturday
morning. Areas of light to moderate snow north of the low will
impact Idaho County and Lemhi County into southwest Montana. There
has been a subtle increase in expected precipitation amounts with
general snow amounts of 1 to 3 inches, isolated higher amounts (3
to 6 inches) on passes. Local road temperature guidance supports
snow impacts to roads from just after sunset lasting through mid
morning on Saturday. Given this slight upward trend in snow
amounts and anticipated impacts, winter weather advisories have
been issued for parts of Lemhi County and southwest Montana. There
is still a question of how far north light snow will stretch but
there is a potential (20-30% chance) for the Bitterroot and
Missoula valleys to see a dusting of snow.

Little change is noted to the Sunday-Tuesday period. The upper
level flow will become westerly on Saturday night and Sunday causing
widespread mountain snow and a very light wintry mix in the
valleys in northwest Montana and north-central Idaho. A strong
cold front is expected to push through the region Sunday night.
This front will cause snow levels to drop to around 2500 feet by
Monday morning. The majority of the Northern Rockies valleys could
experience snowfall by Monday morning, but accumulations should
be relatively light.

Also gusty southwesterly winds are expected to develop ahead of
the front on Sunday and then turn to the west after the frontal
passage. Widespread wind gusts of 20 to 30 mph are expected in the
valleys with the higher terrain having gusts into the 40 mph
range. The combination of wind and snow could create difficult
driving conditions over mountain passes Sunday into Monday
morning. The pass that will have the highest chance for blowing
snow and reduced visibility is Marias Pass Sunday night through
Monday. Also, watch for localized icy roads on Monday morning
behind the front, particularly across southwest Montana.

Showery conditions will persist through Monday into Tuesday as
snow levels remain around 2500 feet, so the potential exists that
the valleys could have additional light snow accumulation.

Although, ensembles continue to support a ridge over the western
U.S. the latter part of next week, there are questions of where
the axis will set up and how stable the strength will be. Recent
trends in deterministic models have been to show a southwest flow
over the Northern Rockies which would allow for periodic light
precipitation and abundant cloud cover, stay tuned.


&&

.AVIATION...As partial clearing occurs, areas of fog and low
stratus are a concern for KGPI and KMSO through late morning. A
mid-level circulation is still expected over the Snake River Plain
this afternoon, shifting into southeast Montana by Saturday
morning. Areas of light to moderate snow north of the low will
bring visibility and ceiling reductions from Idaho County eastward
into southwest Montana late this afternoon through Saturday
morning. There is still some question on the northward extent of
the light snow, KHRF could be impacted by as well. Additionally,
northerly winds of 10-20 kts will impact Lemhi County and
Southwest Montana as the surface low strengthens.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory from 5 PM this afternoon to 9 AM MST
     Saturday for Butte/Blackfoot Region.

ID...Winter Weather Advisory from 5 PM this afternoon to 9 AM MST
     Saturday for Eastern Lemhi County.

&&

$$