Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 251047

Area Forecast Discussion
National Weather Service Missoula MT
347 AM MST Sat Feb 25 2017

...Snow expected Sunday into Monday...

.DISCUSSION...A weak disturbance brought light snow to Butte and
portions of Lemhi County early this morning. Another shortwave
trough will swing through this morning and could bring a chance
for flurries in the valleys and a dusting for mountain locations.
High temperatures today will generally be 8 to 12 degrees below
normal for this time of year which ranges from the upper 30s to
lower 40s.

An upper level trough will hug the British Columbia coast as it
tracks southward towards Washington State tonight. Ahead of this
feature, moisture in the form of snow will begin to stream into
northwest Montana by midnight and into north-central Idaho after
midnight. Expect wintry impacts with slick roads tonight through
Sunday morning. Road temperatures will begin to warm above
freezing by late Sunday morning contributing to snowmelt. Another
feature of note will be a Canadian cold front that will be moving
through the backdoor of Glacier National Park and eventually into
the Flathead Valley sometime later Sunday. Model timing of this
frontal feature is in question. At this point we leaned heavily on
the slower timing of the Canadian and high resolution models,
which could mean a period of moderate or perhaps heavy snow
somewhere across northwest Montana Sunday evening. If this
scenario would pan out, roads could get quite slick from snowmelt
freezing into ice under the new snow.

After 5 pm on Sunday, roads will cool enough elsewhere to allow
snow impacts to be possible across much of the region. There will be
intense convective snow showers that develop Sunday afternoon
continuing into the evening hours. These could become an impact
with snow melting on warm road surfaces then freezing. The
Canadian cold front may be able to make it to Ovando and MacDonald
Pass Sunday night bringing snow and colder temperatures.

The Northern Rockies remain under northwest flow Monday through
next weekend. While not particularly moist, there will be enough
moisture to cause showers, especially in the mountains. Afternoons
will also likely be unstable due to the increasing sun angle and
length of day causing showers to increase. Main concerns will be
with road conditions changing quickly throughout this period.
Showers during the day will likely have little impact due to the
effects of the sun on the ground, however, once the sun goes down
road conditions could change very quickly.

There are some indications of a strong and very, very windy cold
front early next week. Confidence remains low because model
solutions have been changing with the timing and strengths, but
it is hard to ignore because it keeps coming up, so expect to hear
more about this system in upcoming forecasts.


.AVIATION...The weather disturbance responsible for KBTM`s snow
this morning will move out of the region by 25/1500z. Another
shortwave trough will move through the region by 25/1800z and will
bring scattered snow showers or flurries across the Northern
Rockies. Other than a few mountain obscurations, VFR flying
conditions are expected this afternoon. Strong westerly winds
will pick up over the Continental Divide by Glacier National Park
after 25/2100z and will diminish somewhat by 26/1200z. A potent
weather system will bring mountain and valley snow, reduced
visibility and ceilings across northwest Montana by 26/0900z and
then affect the remainder of north-central Idaho and western
Montana into Sunday.



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