Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 202129 CCA

Area Forecast Discussion
National Weather Service Missoula MT
249 PM MDT Wed Sep 20 2017

...Accumulating snow down to around 5000 Feet Thursday night and
Friday southwest Montana...

.DISCUSSION...A very moist west flow will gradually decrease over
north central Idaho and southwest Montana tonight. However,
additional light to moderate snow accumulations can be expected
at and above 5000 feet this evening. Over northwest Montana, the
showers should actually increase into this evening and persist
into Thursday morning. The snow level should lower to 3500 to 4000
feet making some mixture of light snow possible in some valleys
with showers by early Thursday morning.

A very cool and moist atmosphere will cover the region Thursday
with relatively low snow levels. The difference compared to the
past few days is the precipitation should be more scattered and
light from the Camas Prairie and Orofino eastward across western

A cut-off low pressure system still looks likely to develop over
eastern Idaho and southwestern Montana late Thursday evening, and
linger over the region through the day on Friday. The low is
expected to pull in enough cold air, to allow for accumulating
snow to develop across southwestern Montana and Lemhi County down
to around 5000 feet. Snowfall is currently forecast to begin
falling soon after midnight Thursday night and continue through
much of the day on Friday. Details in amounts are a little
uncertain at this time, but heavy mountain snow in the
Anaconda/Pintlers and along the Continental Divide of southwestern
Montana and Lemhi county seems likely right now.

A ridge of high pressure will begin to build over the region for
the start of the weekend and next week, that will allow conditions
to clear out. Due to the cooler air mass that will be settling in
behind the departing low, we could be looking at our first
widespread frost/freeze in the valleys of western Montana and
north-central Idaho (With exception of Orofino and Riggins areas)
Saturday and Sunday mornings. Those that haven`t seen a frost or
freeze, will likely experience one by this weekend.


.AVIATION...Periodically lowered ceiling and visibility will be
likely for all area terminals tonight. Scattered showers will
further moisten the low level air mass and produce areas of low
stratus and fog overnight into early Thursday.



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