Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 202059

Area Forecast Discussion
National Weather Service Missoula MT
259 PM MDT Sun Aug 20 2017

...No clouds expected for the eclipse, though smoke will persist
in places...

.DISCUSSION...The combination of high clouds from a weak
disturbance passing over Montana and Idaho to the region and kept
temperatures largely in check today. Clearing is expected after
midnight with many valleys becoming quite cool by Monday morning.
This will once again place the Missoula Valley in a favorable
pattern for smoke to accumulate from nearby fires.

Fortunately we are expecting NO CLOUDS for the eclipse late
tomorrow morning. And while the thick smoke is unlikely to
completely obscure the sun, except very near wildfires, it will
provide a unique viewing opportunity across much of the Northern

High pressure will continue to strengthen on Tuesday and Wednesday
with afternoon temperatures quickly rising above normal. But the
longer nights combined with overnight clearing should produce cool
mornings in many valleys. And of course smoke will continue to be
an issue with air quality likely to degrade each day as stable
conditions persist. The atmosphere is likely to start mixing
better late Wednesday afternoon with the gradual increase in
mid/high level moisture producing some afternoon clouds. There may
even be a stray thunderstorm across Central Idaho late in the
day. However better chances come into the forecast overnight as
models all agree on an area of monsoonal moisture working its way
through Oregon and into Idaho and Montana by Thursday.

Thursday could be a particularly interesting day across the
Northern Rockies with models in really good agreement showing a
strong cold front passing through the region during the afternoon.
Unlike previous cold fronts, this one appears to be quite unstable
and convective, meaning it will likely bring gusty winds and
thunderstorms. The threat for severe storms does not appear all
that great, though some thunderstorms along the front could easily
produce wind gusts of 40 to 50 mph. There will be some rainfall
with these storms, but their forward motion will keep
accumulations spotty.

Behind the cold front conditions quickly turn dry with gusty winds
likely to persist into Friday afternoon. Unfortunately models
indicate that high pressure is once again likely to rebound
bringing warmer and drier conditions back into the forecast for
next weekend.


.AVIATION...Breezy afternoon winds will help mix and dilute the
smoke which is reducing visibility at KMSO today. However smoke
will return overnight and by 21/1400z visibility as low as 1 mile
is expected. Elsewhere expect few issues to aviation with some
light afternoon breezes for the next few days.



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