Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 271050

Area Forecast Discussion
National Weather Service Missoula MT
350 AM MST FRI NOV 27 2015

.DISCUSSION...The Northern Rockies remains parked between strong
high pressure over British Columbia and a large low pressure
system, the same one which brought snow and cold to the area two
days ago, rotating near Nevada and Utah. In between these two
weather features lies Montana and Idaho under a clear and very
stable air mass. This has allowed morning temperatures to once
again plummet and subsequently strengthen existing inversions.
Those valleys in NW Montana where low stratus clouds are already
fixed in place (Mission/Flathead/Eureka Valley) will see little,
if any improvement today. High temperatures, like the atmosphere,
will be largely stagnant and fail to see much of a rise throughout
the day.

Elsewhere the plague of low clouds and fog will likely spread
and begin to impact people living in the Missoula, Bitterroot and
Potomac Valleys, at least on a limited basis. The expanse of fog
and low stratus are likely not to stop this morning given that the
overall pattern will remain stuck in place through at least Sunday
morning. Temperatures remain the most challenging part of the
forecast and have largely gone with a persistence styled forecast.
Mountain locations and high elevations valleys (like Butte) who
have trouble maintaining inversions will see pleasant afternoon
temperatures following very cold mornings. However inverted
valleys are likely to see limited heating potential, especially
those with stratus fixed in place.

Next week models are starting to come to agreement for a system
mid to late next week. The change in the pattern will mean a
return to southwest flow aloft and southerly flow at the surface.
This will help gradually erode the pools of cold air that are
establishing in the valleys and warm the valleys. It will also be
our next chance for some snow, though it doesn`t look like it will
be a big storm at this time.


.AVIATION...Stratus will continue to plague KGPI with low ceiling
heights through at least the next 24 hours with little significant
improvement. Meanwhile area webcams in the vicinity of KBTM show
freezing fog and/or stratus developing. While this may not pose a
multiple hour impact to the airfield, low clouds and/or fog will
be present in the vicinity of KBTM throughout the morning before
dissipating. Conditions at KMSO are a bit more challenging to
predict. However all indications support freezing fog and/or
stratus developing by sunrise and persisting till around mid
morning. Even thicker and perhaps more long lasting low clouds
stratus and fog are likely to affect these air fields tonight
through Saturday. KSMN will remain entrenched in a deep set
inversion and in time, fog is likely to form. However that is not
likely to occur until Saturday morning.



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