Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 172131
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
231 PM MST WED DEC 17 2014

...SNOW TURNING TO HEAVY RAIN THIS WEEKEND IN CENTRAL IDAHO...

.DISCUSSION...For the end of the work week, two weakening weather
systems will move through north central Idaho and western
Montana. The first shortwave will impact far northwest Montana
late tonight into Thursday. Due to weak forcing, snowfall totals
are expected to be under an inch for all but the highest terrain.

A more substantial system moves in Friday morning bringing
accumulating snowfall to the passes between Montana and Idaho,
especially Lookout and Lolo passes, each of which could see 2 to
3 inches. As it`s predecessor, this system loses steam as it
crosses western Montana, and valley locations should expect only
light rain.

Saturday night through Monday morning an atmospheric river will
impact central Idaho and western Montana. Snow levels will start
out around 3000 ft Saturday afternoon and rise to around 5000 -
6000 feet by Sunday night. As the forecast stands, this will cause
3 to 7 inches of heavy wet snow by Sunday morning to impact
mountain passes. Lookout and Lolo passes will be most affected,
with snow on the lower end of the range affecting Marias and Lost
Trail passes. While forecast confidence is high with the timing
and high moisture for this system, it is not as good with the snow
levels, and as a result confidence is below average for the snow
amounts at the passes.

During the day Sunday, snow levels will rise causing snow to turn
to rain in many areas, generally causing uncleared roads to be a
wet slushy mess. By Monday, 2 to 3 inches of rain is expected in
the Clearwater Mountains and Bitterroot mountains of central
Idaho. The excessive rain combined with temperatures around
freezing will make falling rocks and debris on roads a risk,
especially along highway 12 in central Idaho.

The rest of the week looks showery with the next significant
disturbance coming in around Christmas. This will be a much cooler
system that will likely cause some snow and travel difficulties.
There is a lot of uncertainty associated with the strength and
timing of this system, but models across the board have been
consistent in bringing something through around Christmas. So the
odds of a white Christmas are improving!

&&

.AVIATION...Satellite imagery shows high and mid-level clouds
moving into the area, and this trend is expected to continue
through the rest of the evening. Currently northwest Montana has
the best chance of seeing precipitation in the next 24 hours.
Models depict intermittent snow starting at KGPI around 18/1200Z,however,
accumulations are below an inch.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

$$



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