Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 291040

Area Forecast Discussion
National Weather Service Missoula MT
340 AM MST SUN NOV 29 2015

.DISCUSSION...Strong valley inversions and the accompanying low
stratus clouds and fog will remain the leading weather story
through about mid week as high pressure continues its dominant
hold over the Northern Rockies. The valleys across NW Montana will
remain stuck in this soupy mix of stratus and occasional freezing
fog with little chance for hope of improvement through at least
Tuesday evening. Elsewhere the biggest challenge has been
determining where stratus and/or freezing fog will form next and
managing the subsequent temperature trends. Observations of air
temperature and dewpoint values seem to support further
thickening of stratus and freezing fog throughout the Missoula,
Bitterroot and Potomac Valleys this morning. And unfortunately,
the data along with past practices would also suggest that once
the foggy, stratus combination sets in, it will be hard to scour
out until we see the passage of an active weather feature.

Changes are on the horizon by Wednesday, however, as a weak
weather system approaches the Northern Rockies. This will help to
slightly modify some of the valley cold pools and stratus/fog in
place by streaming in clouds and southwesterly flow, as well as
light precipitation to northwest Montana and central Idaho.
Valleys in northwest Montana could experience frozen or freezing
precipitation issues as below freezing temperatures continue to
linger. A stronger system is expected Friday that has the
potential to bring more widespread rain/snow to region. This
disturbance will further help to erode the valley inversions in
place and allow temperatures to finally reach 30s and low 40s for
many valleys by Friday. Lastly, another disturbance with
additional rain and snow is forecast to approach late
weekend/early next week, though much uncertainty still exists on
timing and strength at this time.

.AVIATION...A persistent low stratus deck will remain fixed in
place at KGPI into the foreseeable future. At KMSO, the stratus
deck and patchy fog are expected to develop this morning and
linger throughout much of the day. KBTM will continue to battle
drifting fog and stratus during the morning hours with conditions
improving by the afternoon. And at KSMN some fog is expected to
develop by the morning, but dissipate by late morning/early



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