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fxus65 kmso 192142 
afdmso

Area forecast discussion
National Weather Service Missoula Montana
242 PM MST Tue Nov 19 2019

Discussion...

A storm system drawing snow and cold air over the northern
rockies through Wednesday remains on-track, however timing
differences among moisture and cold air have altered the weather
impacts present during this time. For the Glacier park region,
including Highway 2 (essex to marias pass), the delay of cold air
over the Continental Divide has resulted in lowered expectations
of snow, blowing snow, and low visibility. East winds will spread
from The Divide, moving west and south this evening through
Wednesday afternoon. The transit of these east winds may end up
being the prime Focal Point for 2-3 hour period of light snow,
favoring the Lower Clark Fork region, including Highway 200 west
of Ravalli, Highway 93 Arlee to Evaro hill, and I-90 west of the
Missoula valley. This convergent feature may extend as far south
as the Idaho Camas Prairie (including whitebird grade). We will
be watching closely to assess the potential of impactful winter
weather.

Snow will linger over the northern rockies through Wednesday,
with mountain passes most favored for light (if any) snow
accumulation. Daytime temperatures will cool 10 to 15 degrees over
those of today, with east and northeast winds continuing to be
present across the region. Much of the east winds should subside
by sunset Wednesday.

A "bubble ridge" of high pressure will begin to build over the
Pacific northwest and northern rockies on Thursday as low pressure
spreads widespread precipitation across the desert southwestern
states. This high pressure over low pressure pattern is likely to
persist for at least a few days (through Saturday morning),
likely leading to enhanced valley cold pool inversions,
deteriorating air quality and a persistently gray valley sky.
Meanwhile, above the inversions, seasonably warm afternoon
temperatures and an abundance of sunshine.

However, all the models agree that by Saturday a series of upper
level disturbances will knock down the high pressure ridge and
leave northwest flow aloft in place across the region in their
wake. This pattern, which appears to be present through much of
next week, will be very favorable cold air maintenance as well as
snow production (especially in the mountains).

Thanksgiving outlook: while still too early to place much
confidence in the models, the trend is leaning towards a cold,
potentially snowy weather pattern for Wednesday through the
Holiday weekend.

&&

Aviation...
precipitation will stick around through Wednesday morning, leaving
plenty of moisture available to decrease visibility, lower
ceilings, and obscure terrain. Patchy fog or low stratus is a
strong possibility on Wednesday morning at all terminals. However,
moderate winds could hamper fog formation at kgpi. Skies clear
out across the forecast area by Wednesday afternoon and usher in a
return to VFR conditions.

&&

Mso watches/warnings/advisories...
Montana...Winter Weather Advisory until midnight MST tonight
Butte/Blackfoot region...Potomac/Seeley Lake region.

Winter Weather Advisory until midnight MST tonight West Glacier
region.

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