Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 212212

Area Forecast Discussion
National Weather Service Missoula MT
312 PM MST Wed Feb 21 2018

.DISCUSSION...A weak wave is exiting the region over Lemhi County
this afternoon. This system brought some light snow to Lost Trail
Pass and areas near Salmon. Other than that there is a mixture of
sun and clouds across the remainder of the region. Satellite
imagery reveals high clouds beginning to float over Idaho. This is
the leading edge of the next system that will affect the southern
half of our area Thursday.

Light snow will begin to fall across southwestern Idaho County by
early Thursday morning and then spread eastward throughout the day
affecting Elk City, Dixie and Lost Trail Pass. There is low
confidence if the southern Bitterroot Valley including Hamilton
will see anything out of this low pressure system which will dive
south into southern Idaho Thursday evening. Could see a dusting to
a half inch in the Grangeville area, possibly 1 to 3 inches for
Riggins, Elk City, Dixie, and Lost Trail Pass. Because this system
becomes cutoff for a period Thursday afternoon centered over
east-central Oregon into Idaho, there is a chance that snow
intensities could become moderate affecting Elk City, Red River
Hot Springs and even the lower elevations like the Salmon River
Valley. Also this system will help to increase the northerly wind
gradient across the region. Some of the typical gaps and canyons
will see the best chance for some possible gusts between 10 to 20
mph which would equate to wind chills near zero or below zero.

Multiple shortwave and large scale troughs are expected to bring
areas of snow during this weekend. While cold on Saturday the
combination of weak moisture and lift should make for widespread
snow. North-central Idaho and the mountain passes along the ID/MT
border are best situated to see the highest snow amounts with 4-6
inches in the valleys and 8-12 inches in the mountains. A couple
of inches of snow are possible for western Montana by late
Saturday. The more robust weather system remains on track to
arrive Sunday afternoon. This trough will bring increased
southwest winds and a better moisture feed than during the early
weekend trough. The highest snow amounts are currently likely to
be in north-central Idaho and northwest Montana. Temperatures will
moderate Sunday so many places may return to above freezing
before the cold front passes Sunday night, so slick roadways are
possible during Monday morning.

Long-range models are hinting at a showery pattern to continue mid
to late week, but become much variable thereafter on whether a
warmer southwesterly flow returns to the region. Therefore, have
kept a chance of precipitation across the area with slightly
below-normal temperatures.


.AVIATION...A weak shortwave is exiting the region near Lemhi
County this afternoon and has resulted in light snow. This feature
will exit by 22/0000Z. With a very brief upper-level ridge moving
over the area tonight, there will be a mixture of low stratus and
possibly some ground fog through 22/1500Z but confidence is not
very high on which terminal will see the best chance. A trough
will dig south into Washington and Oregon and begin spreading snow
into southern Idaho County by 22/06000Z. Light to moderate snow
will bring lower visibility and ceilings between 22/2100Z and
23/0300Z mainly across the southern half of Idaho County and Lemhi



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