Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 171057

Area Forecast Discussion
National Weather Service Missoula MT
357 AM MST Tue Jan 17 2017

...Freezing Rain possible for the Wednesday morning commute...

.DISCUSSION...Passing cloud cover has helped temperatures to be
slightly milder than the last few mornings. This trend will extend
into this afternoon, so high temperatures will be a fair amount
warmer today in many places. Missoula and Salmon have too much
cold air trapped in the valley for much warming so high
temperatures will only be slightly warmer.

Winds are beginning to increase in the Camas Prairie of Idaho,
southern Lemhi County Idaho, and points along the Continental
Divide. While winds are increasing, some of the temperatures are
not, so sub zero wind chills are occurring this morning.

A weather disturbance, currently just offshore of Oregon will
traverse across northwest Montana later this afternoon. There
could be enough moisture with this feature to support light snow
or even a mixture with sleet which could cause some slight
nuisance for the evening commute especially for the Flathead and
Mission Valleys. There is a slight chance that portions of
western Clearwater County, Idaho could receive light freezing rain
this afternoon but confidence is low.

The next moisture influx will occur tonight through Wednesday with
the bulk of the precipitation falling over north-central Idaho.
The biggest impact with this system will be chance for freezing
rain. Many valleys in both Idaho and western Montana have the
potential of experiencing slick road conditions. Also another
impact will be the possibility of ponding of water over western
Clearwater County and maybe portions of northwestern Idaho County.
The temperature forecast has been very tricky because there are
deep cold pools in the valleys that will have to be eroded
eventually. Some places could jump into the 30s and 40s while
others could stay in the 20s for highs Wednesday. Freezing rain
could continue in some valley locations into Wednesday
afternoon, but confidence is not very high on specifics.

For Thursday we are still expecting a weak cold front to move
through. Temperatures are expected to be in the 30s to near 40.
Showers are also possible across north-central Idaho and in the
higher elevations across northwest Montana.

The overall depiction of the weather pattern for Friday, the
weekend, and early next week has not changed much with a general
cool trough to be over the region. Depending on the amount of
cloud cover, valley locations may have cold mornings during the
end of the week and weekend but high temperatures should not be
as cold as we have been seeing. There are differences in timing
and strength of any particular shortwave in the extended forecast
period, so keying in on any one specific day where the highest
chances for snow will be is challenging, but as of now Sunday
into Monday has a better chance for a more organized system.


.AVIATION...Low stratus and fog continue to exist in the Flathead
and Mission valleys, which has been dense at times overnight. The
stratus is forecast to remain through the morning, though, should
slowly lift in the Flathead Valley. The Mission Valley is more
likely to keep the low cloud cover through today. Increasing mid
and high level cloud cover is forecast for north central Idaho
and western Montana today as a warm weather system approaches, so
mountain obscurations will become common. Light precipitation will
begin to fall in northwest Montana and north central Idaho this
afternoon but the main area of precipitation is not forecast to
arrive until tonight. The warm nature of the upcoming weather
system along with strong valley inversions has the tendency to
produce a variety of precipitation types from snow to sleet and
freezing rain on Wednesday.


MT...ID...Air Stagnation Advisory until 10 AM PST this morning Lower Hells
     Canyon/Salmon River Region...Northern Clearwater
     Mountains...Orofino/Grangeville Region...Southern
     Clearwater Mountains.


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