Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 201030

Area Forecast Discussion
National Weather Service Missoula MT
330 AM MST Mon Feb 20 2017

.DISCUSSION...Embedded disturbances in southwesterly flow will
work with abundant moisture to produce several rounds of
precipitation today and Tuesday. The first wave of moisture will
arrive this morning with snow levels initially starting relatively
low generally near valley floors with some very light valley snow
accumulations possible before snow levels quickly rise by late
morning. Mountain passes such as Lookout, Marias, Lolo, and Lost
Trail will see 2-4 inches of snowfall today with roadway
conditions alternating between wet and slick, snow packed. Also
watch for a few thunderstorms across mainly central Idaho this
afternoon, which could produce gusty winds, small hail, and brief
burst of heavy precipitation.

Precipitation will turn more showery late today and continue
tonight with mountain passes occasionally seeing brief periods of
snowfall while valleys experience a primarily light rainfall.

By early Tuesday morning the next surge of moisture arrives
resulting in a period of widespread light to moderate valley
rainfall. This rain combined with mild temperatures will enhance
valley snow melt and may lead to ponding on roadways and property
with debris flows possible along susceptible travel corridors
(such as Hwy 12 in Idaho). Mountain passes will also see another
round of moderate to occasionally heavy snowfall with general
snowfall of 3-6 inches. Gusty winds are also expected Tuesday
afternoon across Lemhi County which may lead to some drifting of
any new snowfall.

Precipitation will become showery again late Tuesday with a cold
front passage overnight dropping snow levels to valley floors.
Some light valley snow accumulations are certainly possible,
resulting in changeable driving conditions.

A much cooler air mass will start to track into the Pacific
Northwest by Wednesday, and remain over the Northern Rockies
Wednesday into the early weekend. Periods of snow showers are
expected daily under this pattern, though only minor snow amounts
are anticipated at this time. The main concern will be the
temperatures returning, and generally remaining, below freezing
by Wednesday night into the weekend. Night-time temperatures will
likely drop into the teens and single digits for most valleys,
with the higher elevation valleys of western Montana possibly
reaching below zero. An active cool and snowy pattern will
continue early next week.

.AVIATION...Patchy fog will be possible this morning ahead of a
warm front which will lift northward across the region today. This
front will bring periods of rain/snow to terminal sites, leading
to reduced visibility and lowered ceilings at times, along with
mountain obscurations. Precipitation should become more showery
later this afternoon with a few showers capable of gusty winds.
Another band of widespread precipitation is expected Tuesday
morning. Low level wind shear of 30-35 kt may also be problematic
today, especially for KMSO.



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