Weather Service Report


322 
FXUS65 KMSO 231010
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
310 AM MST Sun Feb 23 2020

.DISCUSSION...A cold front is coming and bringing wind and snow
with it. Southwest winds will increase ahead of the front today
with the front arriving this evening and overnight.

Snow with the front will only last a couple of hours, maybe less,
for most locations except the mountains. The Clearwater,
Bitterroot, Mission, and Swan mountains can all expect several
inches of snow over 24 hours whereas most valley locations are 
only expected to get less than an inch of snow in 1-2 hours.

For west central and southwest Montana and Lemhi county, ID, the
bigger impact may be winds. Broadly, we expect winds 20 mph with
gusts into the 30s as the front moves through. However, the
strongest winds are expected in Lemhi county, ID. The town of
Salmon will be somewhat sheltered, but winds will increase rapidly
outside of town and higher in the terrain where winds 30 mph with
frequent gusts over 40 mph are expected in the evening and
overnight.

Finally, after the front passes conditions become unstable and
there is concern for potential snow squalls in southwest Montana,
especially the areas around Butte and Anaconda. These small,
intense snow showers can be dangerous because they can cause a
rapid degradation of conditions over a short distance, especially
at highway speeds. We'll be watching these closely and will issue
snow squall warnings if warranted.

By Tuesday, models build a ridge over the region for the remainder
of the week. There will be a few disturbances moving through the
ridge that may cause some light mountain showers or clouds, but
minimal impacts from weather are expected. Some very nice days, 
potentially warming into the 50s in many locations, are expected 
mid to late next week.

For next weekend models have diverged with ensembles clustering
around two forecasts for the region. The majority, close to 65
percent, of the ensembles have another trough and cold front
system moving in for the weekend. A significant minority are
indicating a strong ridge continuing over the region. The current
forecast is a compromise with a chance of precipitation and above
average temperatures.

&&

.AVIATION...Today will start out under VFR conditions, but weather
will deteriorate with cold front passage later in the day. Hi-res
models show a long, well-formed band of snow showers moving 
northwest to southeast along the cold front. These showers should
arrive at KGPI and KMSO by about 23/20Z, while KBTM and KSMN will
see impacts by about 24/00Z. All terminals should expect a 
decrease in ceiling and visibility, as well as strong, gusty 
winds, with the frontal passage. Snow and gusty winds will 
continue into Monday morning. 

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory from 2 PM this afternoon to 11 AM 
 MST Monday West Glacier Region.

ID...Winter Weather Advisory from 1 PM this afternoon to 10 AM PST 
     Monday Northern Clearwater Mountains...Southern Clearwater 
     Mountains.

     Wind Advisory from 7 PM this evening to 2 AM MST Monday Eastern 
     Lemhi County...Western Lemhi County.

&&

$$

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Western Regional Climate Center, wrcc@dri.edu