Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 051417 AAA
AFDMSO

Area Forecast Discussion...UPDATED
National Weather Service Missoula MT
817 AM MDT SUN JUL 5 2015

.UPDATE...A Lake Wind Advisory has been issued for Flathead Lake
for continued strong northeast winds causing choppy conditions
through out the daylight hours today. Winds of 15 to 20 mph, with
gusts to 30 mph are expected throughout the day. Wave heights will
be in the 2 to 3 foot range, with the largest waves on the western
and southern portions of the lake. The pressure gradient will
slowly relax as evening approaches, leading to weakening winds and
subsiding waves.

&&

.PREV DISCUSSION... /ISSUED 418 AM MDT SUN JUL 5 2015/

DISCUSSION...

A complex weather pattern has evolved early today over the
Northern Rockies. An approaching upper-level trough sliding
southeastward through southern BC Canada is pushing a vigorous
cold front out in advance through western Montana, and has
provided enough lift for some showers and a few overnight thunderstorms
across northwest Montana. Meanwhile, an area of enhanced moisture
is moving up from the south. Together, these features will bring
scattered showers and a few thunderstorms to much of western
Montana and parts of central Idaho into this afternoon, along with
drastically cooler temperatures and breezy winds. Models show
some instability increasing from Lemhi County Idaho to southwest
Montana this afternoon, and thus that region will likely be the
focus of thunderstorm development late in the day. Lightning and
gusty winds look to be the main threat. Drier and more
stable air will sweep in from the northwest after the trough axis
passes midday, which will suppress showers from northwest to
southeast during the day. Meanwhile, many locations in western
Montana will see gusty east winds, especially in places like
Hellgate Canyon where the wind direction lines up with the
terrain. The cold front looks to weaken and stall near the MT/ID
border, so central Idaho locations such as Grangeville and
Orofino will not see as much relief from the heat.

The Glacier NP area will see perhaps the most drastic difference
in weather today, with temperatures running 15-20 degrees cooler
than the previous day and intermittent showers for the first half
of the day. East winds will be gusty at times as well. Holiday
visitors should be prepared for rapidly changing weather
conditions.

Drier and quieter weather is expected Monday. Some chance of
showers/thunderstorms will linger from Lemhi County through
southwest Montana. East winds will persist over western Montana,
though not as gusty as Sunday.

Another backdoor front will move in on Tuesday and will bring the
threat of thunderstorms across western Montana Tuesday afternoon.
The main threat will be lightning strikes, gusty winds and brief
heavy rain.

A brief ridge of high pressure will begin to build on Wednesday
and will bring warmer temperatures and increasing thermal belts.
Thursday looks to be the warmest day with highs in the mid 90s
for many areas. Forecast models have been hinting at a more active
thunderstorm pattern beginning on Friday, so stay tuned for
updates.

AVIATION...Much cooler and breezier conditions today for most
terminals. KGPI may be impacted by thunderstorms in vicinity
during the morning hours. KBTM and KSMN could also see showers or
thunderstorms in the afternoon, with an outside chance at KMSO.
Gusty east winds will affect much of the area today. KGPI and KBTM
will see the strongest winds with 20-30 kt gusts through mid-
morning. KMSO will likely experience 20-30 kt gusts late this
morning, lasting through the afternoon.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...LAKE WIND ADVISORY until 9 PM MDT this evening Flathead/Mission
     Valleys.

ID...None.

&&

$$


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