Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 202205

Area Forecast Discussion
National Weather Service Missoula MT
305 PM MST Sat Jan 20 2018


A barrage of weak storm system embedded in westerly flow aloft
will move across the Northern Rockies during the next week.
Tonight and Sunday morning, a weak storm system currently over
central Washington will increase chances of snowfall for higher
elevations of north central Idaho and west central Montana. Travel
impacts will be minor due to minor slick spots that develop. Up
to a couple quick inches of snow over area mountain passes and a
heavy dusting for some valley locales is most plausible. Models
are a bit unsure about southwest Montana seeing some brief snow as
well, however the trajectory of the upper level circulation does
suggest limited snowfall during the wee hours of Sunday morning.
Patchy freezing fog will be possible in the wake of these light
snow bursts.

A slightly more significant storm system is anticipated to bring
widespread light accumulations to the Northern Rockies Sunday
night through Monday midday. Models have trended weaker for the
cold front feature associated with this system, which would result
in lower snow amounts than previous forecasts. Realistically, up
to a couple inches snowfall will occur at low elevations, while
ID/MT border passes will see up to 6 inches. The main impact will
slick roadways, mainly near the mountain passes, due to
accumulating snow.

Model guidance continues to trend the storm system projected near
the Northern Rockies middle of the week even further into Thursday
than previous. The cold front associated with this system now
appears to traverse the Northern Rockies mostly during the daytime
Thursday, however weakened as it is stretched north-south over
time. The net effect of the cold front being stretched this way
will be to weaken it and thus limit snowfall. That said, it`s
another one of those widespread light snow events, with a quick
accumulation of a few inches over valleys and 4-8 inches at the
mountain passes. Considering the trend of models to delay and
weaken the midweek system, confidence is a bit low for this

The westerly flow aloft pattern appears to continue all the way
through next week and being. The implications of the persistent
pattern: occasional light snow events, seasonal cool temperatures,
episodes of patchy valley freezing fog, and plenty of cloudiness.


.AVIATION...Variable clouds and a weak storm system will move
through the Northern Rockies air space during the next 24 hours.
The weak storm system current over central Washington will drift
across north central Idaho and west central Montana overnight,
possibly impacting KGPI, KMSO, and KBTM with brief snowfall
21/0000Z through 21/1500Z. Freezing fog potential is a bit low,
but most plausible in the 21/0900Z through 21/1800Z. Otherwise,
occasional terrain obscurations will exist throughout the region.



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