229 
FXUS65 KMSO 061028
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
328 AM MST Sun Nov 6 2022

...PERIODS OF SNOW...WIND...AND COLD TO IMPACT THE NORTHERN
ROCKIES THOUGH MIDWEEK...

.DISCUSSION...Scattered snow showers and bands continue to develop
and stream over west-central and southwest Montana, as well as
north-central Idaho this morning. Slick roads and reduced
visibility can be expected along area roadways until sunrise this
morning. Additional accumulations will vary, with isolated areas
receiving up to an additional inch or two. The Winter Weather
Advisory has been extended a couple more hours, until 8AM MST to
account for the continued showery activity.

By mid morning, most locations will see a break in the active
weather as a low amplitude ridge of high pressure moves over the
region. The initial push of an arctic airmass will begin to make
its way over the Continental Divide late morning and early
afternoon, producing gusty east-northeast winds from Marias Pass
to Columbia Falls. This initial intrusion of cold arctic air could
create some light upslope snow from Marias Pass to West Glacier.

The main surge of the arctic airmass will begin to push through
northwest Montana this evening, and will gradually move southwest
to the Montana/Idaho border by Monday morning. The cold airmass
coupled with the gusty easterly winds, will create below zero wind
chills Monday evening and through the day Tuesday along the
divide. The coldest air is still expected to be across northwest
Montana, where there remains around a 50% chance for below zero
temperatures Tuesday and Wednesday mornings. On the western edge
of the arctic boundary (e.g. west of Highway 93 in western Montana
and north-central Idaho), a surge of moisture rotating around a
large Pacific coast low pressure system, is expected to produce
several inches of snowfall late tonight and through the day
Monday. Expect periods of intense snowfall over mountain passes,
such as Lookout and Lolo, as well as Whitebird Hill and grades
around north-central Idaho. High resolution models also show an
area of intense snowfall developing over Lemhi County by daybreak
Monday, that will also produce several inches of snow.  

Global models and their ensemble members continue to show a mid-
level circulation developing over central Idaho by late in the day
Monday, that is likely to track over southwest Montana through the
day Tuesday. This consolidated area of energy and moisture will
be overrunning the arctic airmass already in place, and will aide
in the development of widespread snowfall across all of the
Northern Rockies. At this time, the more intense snowfall is
likely to be confined to southwest Montana (Butte/Anaconda
Region), and perhaps as far west as the highway 93 corridor in
west-central Montana. Bottom line is, expect bitterly cold
temperatures and periods of snow for most locations for the first
half of this coming week. And travel with emergency supplies 
while on area roadways in case becoming stuck, especially in 
remote areas.

Global models and their ensembles suggest that weak and disorganized 
high pressure will develop over the Northern Rockies late this 
coming week through next weekend, however large differences exist 
among models. Despite fewer than 30 percent of models suggesting a 
weakly forced snow event over next weekend, we cannot discount the 
tendency for light northwest flow aloft to produce long-lasting 
light snow for portions of the region. Either way, temperatures 
colder than the seasonal average appear to stay through at least 
the middle of November.

&&

.AVIATION...Numerous showers and snow bands will continue across
west-central and southwest Montana until around 06/1500Z this
morning. Brief reductions in visibility and bursts of moderate to
heavy snowfall is expected under these showers. Easterly winds
will begin to push into northwest Montana by 06/1700Z this
morning as the initial push of arctic air spills over the
Continental Divide. The arctic boundary is expected to reach KMSO
and KBTM overnight tonight. Bitterly cold temperatures can be
expected for all terminals through at least wednesday this coming
week, with wind chills lowering to below zero across northwest
Montana and along the Continental Divide.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory until 8 AM MST this morning for 
     Bitterroot/Sapphire Mountains...Butte/Blackfoot Region...
     Lower Clark Fork Region...Missoula/Bitterroot Valleys...
     Potomac/Seeley Lake Region. 

ID...Winter Weather Advisory until 7 AM PST this morning for Northern 
     Clearwater Mountains...Southern Clearwater Mountains. 

&&

$$