Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 280812

Area Forecast Discussion
National Weather Service Missoula MT
112 AM MST Wed Feb 28 2024

.DISCUSSION...A deep and broad trough is digging off the West
Coast and causing a ridge to build over the Northern Rockies
today. A tight pressure gradient between the two is driving strong
winds coming off the Pacific Ocean, which is contributing plenty
of moisture. The combination of the strong winds and moisture is
strong enough to be considered an atmospheric river, and it is
impinging on the Idaho Panhandle and northwest Montana this
morning. Due to the building ridge and southwesterly flow, snow
levels are also rising quickly this today. The end result is that
most valleys across the Northern Rockies are warming up enough
that precipitation will mostly fall as rain. The mountains will
see heavy, wet snow as the snow levels peak late this afternoon
between 4,500 ft and 5,500 ft. As a result of the higher snow
levels, the areas impacted by heavy snow will be limited to
mountain passes like Lookout Pass and Lolo Pass and several miles
either side of the passes. These passes will have a lot of lift,
driving heavy snow due to good dynamics from the jet stream aloft,
a fast moving upper and mid-level trough, a sharp temperature
gradient with the surface front, and good orographic lift. Further
to the east, Marias Pass down to MacDonald and Homestake passes
will see brief moderate to heavy snow due to orographic lift and a
tight temperature gradient with the surface front. However, these
locations won`t have the good support at the mid and upper levels
from the trough and jet stream like the western passes do.

The jet stream, fast moving trough, and sharp surface front will
also support strong southerly winds and the possibility of
mountain wave winds on the Camas Prairie in Idaho. All members,
that`s 100 percent of high resolution models in the HREF modeling
system, are predicting wind gusts over 50 mph between 7 and 10 AM
PST on the Camas Prairie around Grangeville, Idaho. Only 25
percent of those models are forecasting winds over 60 mph. Another
area of concern for strong winds is Highway 95 from McCall, ID up
to Grangeville as the canyon in that region is well aligned with
the strong southerly winds and will enhance them.

As the front moves across the region Thursday, expect about 1 to 2
hours of intense rain and/or snow along and just behind the front.
Due to the warm temperatures most of the day ahead of the front,
we are not expecting a flash freeze scenario on the highways.
However, with heavy snow it may accumulate on the roads faster
than it can melt resulting in a wet, compact snow that can be very
slick. With the cooling temperatures and some lingering snow
showers behind the front, road conditions will be a concern
through Friday morning.

For the weekend, the region will remain under a cool trough. With
the longer days and higher solar angle this time of the year, that
will promote unstable, showery, and blustery conditions.

Early next week, ensembles generally agree on another significant
trough and cold front moving through the region, though there is a
lot of disagreement on the timing. So overall, expect active
weather to continue into the beginning of March, though the timing
of impacts remains very uncertain.


.AVIATION...A ridge is building over the region today, but it will
have an atmospheric river associated with it on its northwest
fringes. Snow levels will also be rising due to southwest flow, so
the main impacts today will be occasional light rain, mid-level
ceilings, and mountain obscurations. If valley snow does occur, it
will only be as a temporary shower and will be unable to
accumulate at major area terminals. Snow levels will peak late
this afternoon or evening and a potent cold front is expected for


MT...Winter Storm Warning until 5 PM MST this afternoon for Lower
     Clark Fork Region.

     Winter Weather Advisory until 5 PM MST this afternoon for
     Kootenai/Cabinet Region.

     Winter Weather Advisory from 5 AM early this morning to 2 PM MST
     Thursday for West Glacier Region.

ID...Winter Storm Warning until 4 PM PST Wednesday for Northern
     Clearwater Mountains.

     Winter Weather Advisory until 4 PM PST Wednesday for Southern
     Clearwater Mountains.

     High Wind Watch from Thursday morning through Thursday evening
     for Lower Hells Canyon/Salmon River Region...
     Orofino/Grangeville Region.


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