Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 082136

Area Forecast Discussion
National Weather Service Missoula MT
236 PM MST MON FEB 8 2016

.DISCUSSION...A building ridge of high pressure will dominate the
weather this week. Today, high clouds continue to stream over the
ridge causing the mostly cloudy skies. As the ridge slowly moves
east and strengthens, expect the cloud cover to decrease tonight,
causing mostly clear skies. Valley inversions will strengthen
under the influence of the ridge causing fog and stratus in
western Montana valleys and near Salmon, ID. Air stagnation will
also be a concern.

On Thursday, Pacific moisture begins streaming through the
flattening ridge, bringing more widespread clouds to the area.
These clouds will keep night-time temps warmer, with cooler
daytime highs. By Thursday night, some light precipitation could
move through far northwest Montana, but this feature has trended
weaker over the past couple days. Many areas will likely not see
much improvement to air quality until later in the weekend.

A stronger system on Saturday or Sunday may bring more widespread
light rain/snow and winds to mix out area valleys, thus bringing better
air quality conditions. The overall pattern still favors ridging
past the weekend, so we may quickly slide back into a stagnant
pattern. Take this extended forecast with a grain of salt, since
model uncertainty is high past the weekend.


High pressure will continue to persist over the Northern Rockies,
bringing generally fair weather. Passing mid to high clouds are
expected to decrease enough tonight to allow the potential for low
stratus/fog development at/in the vicinity of KGPI, KMSO, and
KSMN, obscuring terrain and result in reductions in visibility.
Breezy winds will continue over the Continental Divide.


.AIR STAGNATION...A ridge of high pressure will continue cause
stagnation concerns for western Montana valleys and along the
Salmon river in Lemhi county, ID. Friday high clouds will return
ahead of the next system, with Friday night and Saturday being the
best chance of breaking the inversions. Chances of ventilation are
good for northwestern Montana which will take a direct hit from a
shortwave and possibly a cold front. Lemhi County, however,
doesn`t look as likely to ventilate. As the shortwave breaks down
the ridge across NW Montana the ridge will remain dominant farther
south over eastern Idaho.



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