Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 211040

Area Forecast Discussion
National Weather Service Missoula MT
439 AM MDT SUN SEP 21 2014



High pressure currently over the Northern Rockies will be
undercut from the south by the remnant moisture of tropical
system Odile later today through Monday. Showers and thunderstorms
associated with this tropical moisture will spread as far north as
the Swan Range and northern Bitterroot Mountains. Daytime
temperatures will be very warm ahead of the cloud cover today,
with many valley locations warming well into the 80s.
Precipitation will be most concentrated over central Idaho, with
southern Lemhi County having a reasonable chance at widespread
measurable rainfall. The clouds and rain will cool daytime
temperatures somewhat on Monday.

Just as the remnant tropical moisture from Odile clears the
Northern Rockies, the next and relatively impressive storm system
will begin impacting the region on Tuesday. Models have been
depicting a weak and unorganized atmospheric wave on Tuesday,
ahead of the main surface cold front late Thursday. The lack of
robust characteristics within the depicted Tuesday wave suggests
that afternoon showers and thunderstorms will develop mainly over
the high terrain. Skepticism in the timing and placement of model
precipitation is reflected in a precipitation forecast that is
near or below that of climatology on Tuesday and Wednesday. An
increasing pressure gradient ahead of the main Thursday system
will allow winds to increase, maintaining exceptional late
September warmth. It is possible that near record warmth will
develop during Wednesday afternoon at some locations.

Above normal temperatures on Thursday will come to an end by
Friday as an upper level trough nears the area. A cold front will
move across central Idaho by Thursday night and help to produce
showers and possibly an isolated thunderstorm. As the front nears
western Montana, it will slow down a little on Friday and
possibly stall. As the front stalls, central Idaho to northwest
Montana could see showers, clouds and cooler temperatures for much
of the day. There is a chance that southwest Montana will be able
to warm up nicely Friday, and this is reflected in temperatures
trended warmer there. Showers and cooler temperatures are still
possible for next weekend.



High pressure will dominate much of the weather at Northern
Rockies air terminals during the next 24 hours, however clouds
will be steadily increasing throughout the day near and south of
KSMN. This cloud cover is indicative of remnant moisture from
tropical system Odile. Some lower cloud bases in light rainfall
and isolated cloud-to-ground lightning strikes will be probable
south of KSMN throughout the next few days. Wind gusts will
develop suddenly near thunderstorms, however most of the next day
will be devoid of much wind at any air terminal.




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