233 
FXUS65 KMSO 010839
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
239 AM MDT Sat Apr 1 2023

.DISCUSSION...Satellite imagery this morning is depicting a broad
trough of low pressure with its axis along the West Coast. A 
strong cold frontal boundary ahead of the trough will move into 
the Northern Rockies later this morning. A deep plume of moisture
directed into the Northern Rockies is also visible on satellite 
imagery south of the main circulation. The combination of frontal
dynamics and this moisture feed will create favorable conditions 
for wind and precipitation through this afternoon. Snow levels 
will start out above about 4000 feet, keeping snow accumulations 
off of valley floors. The most intense snow will occur along the 
Idaho-Montana border, most notably Lookout Pass, where snowfall 
rates of 1 inch per hour will be favorable (60 to 70 percent 
chance) between mid morning and early afternoon. Expect decreased 
visibility and difficult travel conditions during periods of 
intense snow showers. Strong westerly or southwesterly winds will 
be present with the frontal passage, with gusts of 40 to 50 mph 
over the higher terrain and 20 to 30 mph along the valley floors 
across the entire Northern Rockies today. 

The front will move through southwest Montana late Saturday 
afternoon into early evening. Forecast models continue to support 
the potential for an intense band of snow and wind to develop 
along the front, which could impact the I90 corridor between Deer 
Lodge to Butte to Homestake Pass as well as the Highway 12 
corridor over MacDonald Pass. Conditions in these areas could 
deteriorate rapidly this evening as drifting and blowing snow will
impact visibility. 

By tonight, the initial shortwave trough will move east, while a
second trough of low pressure deepens along the coast of British
Columbia later tonight and on Sunday. This system will bring
continued snow to the Northern Rockies. Though it will not be
packing quite as much of a punch as today’s system, cold air will
already be in place behind today’s cold front, so snow levels will
be low enough for valley snow on Sunday. The southerly track of
this system will also keep the focus for snow accumulations over
north-central Idaho and the Idaho-Montana border including
Lookout, Lolo, and Lost Trail Passes, as well as the Clearwater
and Bitterroot Ranges. Precipitation will stay in the forecast
into early this week as the Pacific trough continues to amplify
into the Great Basin and wraparound moisture makes its way back
into the Northern Rockies. A light at the end of the tunnel is the
chance for a significant warm-up by next weekend. That’s no April
Fools joke.


&&

.AVIATION...A cold front will move across the Northern Rockies
airspace today, bringing a combination of decreasing ceiling and 
visibility due to precipitation and strong winds. Southerly winds
will increase this morning by about 01/1700Z with winds turning 
westerly and gusts reaching about 30-40 knots this afternoon. 
Precipitation type will be mixed, then transitioning to snow 
behind the front. Expect snow to obscure terrain, especially over 
the Clearwater and Bitterroot Ranges. Although wind speeds and 
precipitation intensities will decrease tonight, snow showers will
continue through Sunday.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory from 6 AM this morning to 9 AM MDT 
     Sunday for Bitterroot/Sapphire Mountains. 

     Winter Weather Advisory from 6 AM this morning to 9 AM MDT 
     Sunday for West Glacier Region. 

     Wind Advisory from 9 AM this morning to 8 PM MDT this evening 
     for Flathead/Mission Valleys. 

     Winter Storm Warning from 6 AM this morning to 5 PM MDT this 
     afternoon ABOVE 4000 FEET for the Lower Clark Fork Region.

     Winter Weather Advisory from 5 PM this afternoon to 9 AM MDT 
     Sunday for Lower Clark Fork Region. 

     Wind Advisory from noon today to 8 PM MDT this evening for 
     Missoula/Bitterroot Valleys. 

     Winter Weather Advisory from noon today to 9 AM MDT Sunday for 
     Butte/Blackfoot Region. 

     Winter Weather Advisory from 5 PM this afternoon to 9 AM MDT 
     Sunday for Potomac/Seeley Lake Region. 

ID...Winter Weather Advisory from 5 AM early this morning to 8 AM PDT 
     Sunday for Northern Clearwater Mountains...Southern 
     Clearwater Mountains. 

     Wind Advisory from noon today to midnight MDT tonight for 
     Eastern Lemhi County...Western Lemhi County. 

&&

$$