Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 292004

Area Forecast Discussion
National Weather Service Missoula MT
201 PM MDT FRI AUG 29 2014

.DISCUSSION...High pressure across the Northern Rockies this
afternoon continues to break down and in turn the atmosphere is
starting to show sign of destabilizing through the presence of
gusty winds and some puffy cumulus clouds. However, instability
and moisture are still insufficient to produce anything more than
a slight chance for showers and thunderstorms across Lemhi County
and maybe Glacier National Park near the Canadian border. For the
rest of the area, the chance for showers or thunderstorms will
wait until overnight when an approaching Pacific cold front sweeps
through the region. A round of very early morning showers and
isolated thunderstorms will develop over central Idaho between
12am - 3am and move northeast across parts of west central and
southwest Montana (generally south of a line from Ronan to Seeley
Lake). The most numerous and strongest storms are expected across
southwest Montana (Butte/Philipsburg/Georgetown area) and Lemhi
County in Idaho.

Convection will decrease some to a more showery regime after
daybreak Saturday morning in the cool and breezy post-frontal
environment. However, the atmosphere will quickly grow unstable
once again during the afternoon, promoting gusty winds across all
of western Montana and a return of some shower activity. We could
even see a few embedded thunderstorms with the key threats being
heavy rain and lightning. Again, the focus of strongest storms
will be spread across southwest Montana. The strongest winds are
expected during the afternoon and could result in some enhanced
wave action on area lakes. Currently it appears waves of 2-3ft
will be possible across parts of Flathead Lake according to our
wave model. These winds should start to subside shortly after
sunset as the atmosphere grows more stable. Sunday looks to be
much less showery and windy than earlier model runs suggested,
though a slight chance for light rain showers will remain during
the afternoon. On the other hand, Monday now appears to be the
showery day as the upper level jet passes overhead during the

Tuesday: The upper level flow becomes more westerly and a little
stronger, which will translate to warmer temperatures and gusty
winds across the region. The best chances for precipitation will
across northwest Montana especially across the higher terrain.

Wednesday: A positively-tilted upper trough seems to be the
consensus solution among the weather models. This would equate to
a lower chance for precipitation across central Idaho and
southwest Montana, and higher chances across northwest Montana.

Thursday and beyond: What a change in model solutions in the past
24 hours! They have dropped the upper level low possibility with
its widespread precipitation tune over western Montana and now
have a general trough over WA to CA. Due to this change, we have
started to trend the chance for precipitation lower across
northwest Montana and a little higher over central Idaho and
southwest Montana. Also, have trended warmer on temperatures.
With southwest flow developing, this would be good pattern for
thunderstorm activity especially from central Idaho to southwest


.AVIATION...A cold front passage tonight into Saturday morning
will keep breezy conditions into Saturday. Some shower and
thunderstorm activity is expected ahead of and with the cold
frontal passage, mainly across north central Idaho into southwest
Montana this evening and overnight. Airfields KSMN and KBTM have
the best potential for early morning showers and thunderstorms, though
it may spread north to KMSO. Saturday still looks breezy and
showery with a slight chance for some afternoon thunderstorms.



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