Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 202055

Area Forecast Discussion
National Weather Service Missoula MT
255 PM MDT Wed Aug 20 2014



A deep trough of low pressure from Canada will impact the Northern
Rockies through at least Monday. Anticipate shower and thunderstorm
activity to steadily increase through Friday, with daytime
temperatures slowly decreasing during this time. Relatively cold air
will be drawn across the entire region, most notably over Glacier
National Park and Bob Marshall Wilderness, where snow levels will
reach 6500 feet on Saturday morning. Up to several inches of snow
accumulation at the high elevations will impact back-country travel.
Otherwise and elsewhere, a very cold rain will develop, increasing
the threat for hypothermia for summertime travelers. Considering
that this type of weather scenario is very uncharacteristic for late
August, this weather will be a big impact on hay farmers looking for
some dry, warm weather. Area wildfire activity will likely continue
on a downward trend, as surface moisture and atmospheric humidity
increase. Wildfire smoke will also lessen over time. Finally, be
aware that temperatures on Sunday morning may be sufficiently cold
for frost within high valleys near the Continental Divide. Gardens
near locations like Butte may suffer from such a frost occurrence.

Global forecast models continue to depict fairly stable and
stationary high pressure ridge south of the Gulf of Alaska for the
next 10+ days. The placement of this ridge implies that the Northern
Rockies will continue to see periodic cold storm systems from Canada
with only a few days break in between. This pattern will have huge
implications on whether or not a fire season will remain possible
through September and October. The proof of the fire season impact
will be revealed with the precipitation amounts observed after the
present weather system passes.



Showers and thunderstorms will exist near all area terminals at
times through 21/0300Z. Thereafter, much of the lightning threat
will decrease, but not totally diminish through 21/1200Z. A pretty
consistent stream of moisture will keep showers active throughout
the overnight. Some brief wind gusts may develop near mature
thunderstorms, but will generally gust below 25 knots. Terrain will
be obscured at times and increase in frequency through Thursday.





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