Area Forecast Discussion
Issued by NWS Missoula, MT

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298
FXUS65 KMSO 170930
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
330 AM MDT Tue Oct 17 2017

...Increasing Wind Today, Peaking this Afternoon and Evening...

.DISCUSSION...
A strong westerly jet is still on track to increase winds across
the area today, especially over the terrain and Continental
Divide. Some valleys may be slower to mix out, but valley winds
in western Montana could reach 30 to 40 mph with locally higher
amounts possible this afternoon and evening. Forecasted
precipitation amounts have decreased significantly with this
system, and therefore is not expected to be much of a concern
today as snow levels remain limited to high elevations. Some
hazards from strong wind gusts today are potential tree falls and
power outages, especially over vulnerable/exposed burn scars,
difficult driving for high profile vehicles, and choppy lake
conditions.

Additional wind and high elevation snow will approach mid-day
Wednesday for northwest Montana and the Divide. Rainfall amounts
are likely to remain minimal in the valleys due to shadowing
effects. High temperatures Wednesday afternoon will be slightly
cooler in the wake of today`s cold front.

A shift to southwesterly flow aloft is still anticipated on
Thursday leading to a pleasant fall day with high temperatures
well in 60s and lower 70s. Breezy winds will continue with the
only daytime precipitation chances from Clearwater County across
far northwest Montana.

By late Thursday evening, a strong cold front will begin pushing
into central Idaho/northwest Montana, and continue eastward on
Friday. Forecast models have struggled of late with the timing of
the front but currently agree it will be to the Divide by late
Friday morning. Snow levels will be quite high ahead of the front
but will drop to mountain pass levels behind it, thus snow covered
roadways above 5,000 feet could be an impact as early as Friday
morning. Southerly winds will also be quite breezy ahead of the
front becoming westerly behind it.

Forecast models continue to show a very wet and mild westerly jet
stream focused on the Northern Rockies late Saturday into Sunday.
This type of pattern typically favors north-central Idaho and the
terrain of western Montana for ample precipitation and windy
conditions. The valleys of western Montana will have breezy winds
and will experience rainfall but much less compared to the higher
terrain. Snow levels will likely remain fairly high but could
fall to mountain pass levels at times with roads impacted, while
backcountry users will face frequent wet and raw conditions.

&&

.AVIATION...West wind will continue to ramp up over the
mountain-top level, with 50-60kt wind gusts (or higher) along the
Continental Divide. Wind speeds for TAF sites will reach 20 to 30
kts after 18/1800Z, and peaking in the late afternoon and
evening. Winds could occasionally reach as high as 40 kts at times
for some of the valley locations. Wind speed shear will be a
concern for both KGPI and KMSO this afternoon due to 40-55kt west
winds aloft just above the surface.

Showery weather, mainly over terrain, will spread southward from
northwest Montana with a cold front after 17/2100Z. These showers
are capable of disrupting wind direction and gusts, causing
erratic rises and falls of wind speed in short distances.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Wind Advisory from 3 PM this afternoon to midnight MDT tonight
     Butte/Blackfoot Region...Lower Clark Fork Region...
     Missoula/Bitterroot Valleys...Potomac/Seeley Lake Region.

     Wind Advisory from noon today to 9 PM MDT this evening
     Flathead/Mission Valleys...Kootenai/Cabinet Region...West
     Glacier Region.

ID...None.
&&

$$



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