Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 241109
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
409 AM MST Tue Jan 24 2017

.DISCUSSION...The upper level is becoming northwesterly and will
persist for the next couple of days. A subtle disturbance will be
moving through this flow later today and this evening which will
cause scattered snow showers, especially along the Montana/Idaho
border. Snow amounts will be generally light, less than an inch,
but a few locations could receive a couple of inches by Wednesday
morning. The shower activity will gradually decrease through
Wednesday.

Patchy fog is also a concern for this morning with a few areas,
especially across northwest Montana, experiencing locally dense
conditions. The fog should dissipated by late morning/early
afternoon.

A few showers may remain on Thursday, especially in NW Montana and
along the Idaho/Montana border. However this chance will decrease
significantly after sunset as high pressure builds inland across
the Pacific Northwest. The upper level ridge is forecast to nose
its way over Idaho and Montana throughout the weekend leading to
clear/sunny, seasonably warm conditions in the mountains and
inversions grow significantly stronger within most valleys. At
least patchy freezing fog is to be expected with areas of dense
fog certainly possible under this type of pattern. Temperatures
will be challenging to forecast since the formation of freezing
fog and/or stratus can severely limit the difference between high
and low temperatures. Meanwhile, those locations lacking fog or
stratus will see very cold nights followed by modest afternoon
warming.

So the big question remaining in the extended is when will the
ridge break down or move? Unfortunately, that`s still up for
debate in the models. Global patterns suggest that we`ll be under
this high pressure ridge well into next week. So it would
probably be good idea to plan for continued valley inversions
promoting repetitive impacts from freezing fog. At the same time
air stagnation will likely become a growing issue with a more
prolonged ridge solution certainly further exacerbating air
quality concerns with time.

&&

.AVIATION...Patchy fog will be a concern across west central
Montana into northwest Montana. KMSO and KGPI have the best chance
of being impacted by fog. Snow showers will increase this
afternoon and evening as a subtle disturbance makes its way
through the northern Rockies under northwesterly flow. These
showers will reduce ceilings and visibilities at times.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

$$



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