112 
FXUS65 KMSO 071102
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
402 AM MST Sun Nov 7 2021

.DISCUSSION...The cold front that brought snow to the mountains
last night has moved off to the east and south this morning.
According to webcam imagery, the front brought a quick burst of 1
to 2 inches with gusty winds ranging between 30 and 40 mph in
higher elevations above 4,000 feet. The temperature on top of
Point 6 Mountain, north of Missoula is sitting at 18 degrees as 
of 2 am, 10 degrees colder than this time yesterday. 

This morning's radar is showing isolated showers across the 
region. Showers will persist today, mainly over the mountains 
over northwest Montana. Breezy south to west winds between 10 and 
20 mph are expected through this afternoon. 

An upper level shortwave will move over northwest Montana tonight
into Monday morning. With such a cold airmass in place, snow
showers are possible at most elevations. Places like Thompson
Pass, Lookout Pass, Yaak, US-2 between Libby and Marion, Olney and
the Glacier Park region could pick up a dusting up to a inch and a
half of snow. Upper level ridging will help put a stop to the
shower activity later Monday, but the wind gradient begins to
tighten especially over Idaho in response to a strong low pressure
system offshore of the Pacific coast. 

Easterly winds will mainly be felt in the higher elevations Monday
night, but places like the Camas Prairie in Idaho will see stiff
southerly winds by Tuesday morning. We have raised the forecast
winds there to reflect possible winds near 40 mph between 
Grangeville and Whitebird. There is a chance that the winds could
be a little stronger than that. This could impact high profile 
vehicles traveling US-95. 

Besides the increased winds, a warm front will bring precipitation
to north-central Idaho and along the Idaho and Montana border by
daybreak Tuesday. Snow levels will be around 3,000 feet but will
rise with time. Several inches of snow is possible for mountain
passes along the border. A few valley locations could pick up some
snow, but with warm ground temperatures, it may just accumulate on
grassy surfaces.

A strong cold front is expected to traverse the region by Tuesday
evening and will drop snow levels and bring widespread showers and
gusty winds. More accumulating snowfall is possible, especially 
across north- central Idaho mountains, but also across western 
Montana including valley locations down to 3000 feet. The region 
remains under unstable, cold and northwest flow into Wednesday 
which would keep the chance for rain and snow showers going. 
Clearing is possible by Thursday which would provide cold morning 
temperatures with patchy fog.

What we call a "dirty ridge" is expected by next Friday and
Saturday as subtropical moisture will move around and through the
ridge into the region. As mentioned before, this would bring
higher snow levels, milder temperatures and breezy conditions to
the region. 

There are a few signs that point to unsettled weather with the 
potential for lower snow levels the following week (3rd week of 
November). An arctic airmass will build over interior Alaska into 
the Yukon territory this upcoming week. This cold and dense air 
will eventually want to travel southward. Ensemble models have 
been trending to have more ridging over Alaska which would enhance
this potential. This pattern looks very La Nina-ish. The Polar 
jet across the Pacific continues to be very active and if we can 
get the right combination of Pacific moisture, good dynamics with 
cold, it could get quite interesting around here. Stayed tuned.

&&

.AVIATION...Isolated rain and snow showers are expected across 
the Northern Rockies today. Shower activity could be more
scattered across northwest Montana and confined mainly to the 
terrain. Expect periodic visibility and ceiling reduction. Gusty 
winds will be felt at all the terminals, generally under 25 
knots. An upper level wave will bring more widespread snow showers
across northwest Montana between 08/0300Z and 08/1700Z. GPI may 
experience a passing shower during this timeframe, but confidence 
is higher that the mountains will experience a majority of the 
activity.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory until 8 AM MST this morning ABOVE 4000 
     FEET for the Bitterroot/Sapphire Mountains.

     Winter Weather Advisory until 8 AM MST this morning ABOVE 4000 
     FEET for the West Glacier Region.

ID...Winter Weather Advisory until 7 AM PST this morning ABOVE 4000 
     FEET for the Southern Clearwater Mountains.

&&

$$