Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 190331

Area Forecast Discussion
National Weather Service Missoula MT
931 PM MDT Fri Apr 18 2014

.DISCUSSION...An upper level wave moving through the region has
brought gusty winds near 40 mph across western Montana this
afternoon. Scattered rain and snow showers that are occurring now
will begin to taper off by this evening. There could be periodic
snow showers at Marias, Homestake and MacDonald Passes with a
chance for slush and reduced visibility. Wave heights up to 3 feet
have been observed by a NWS employee near Woods Bay while Flathead
Lake Biological Station weather sensors have measured sustained
winds near 30 mph with higher gusts. Expect winds to diminish
after sunset across western Montana.

A transient upper level ridge will move through on Saturday
providing for a chilly morning giving way to a pleasant day across
the Northern Rockies. High temperatures will rise into the 60s
which will be 5 to 7 degrees above normal for this time of the
year. There will be an approaching frontal system later in the
day and have added a slight chance for showers mainly over the
higher terrain across north-central Idaho Saturday afternoon, but
expect little precipitation.

Saturday Night...A quick moving weather system will offer a chance
of showers to northwest Montana and the Idaho Panhandle overnight.
Most areas will see increasing winds, especially higher terrain
across northwest Montana.

Sunday through Monday...A ridge of high pressure will be developing
over the Northern Rockies region Sunday, eventually moving into
eastern Montana by Monday. This will be a dry period with warming
temperatures. There may be increasing high clouds Monday for some
filtered sunshine.

Monday Night...A deepening low pressure trough will be approaching
from the west with gradually increasing clouds throughout the
night. In addition to clouds, a chance of rain is also in the mix
across Idaho and adjacent Montana zones by morning.

Tuesday-Thursday...Models continue to show a significant weather
system to impact the Northern Rockies beginning Tuesday afternoon.
There are some challenges to how strong the system will be and the
track of the low pressure and precip placement, but the following
discussion describes the best probability of occurrence.

After a nice day with partly sunny skies on Tuesday, the atmosphere
will become conducive for a few thunderstorms to develop ahead of
the main push of energy and moisture. The better locations for
thunderstorms will be central Idaho and extreme southwest Montana.
There is a lot of moisture associated with this system that could
put down very heavy rain in a short period of time. The potential
for rock and mudslides along highway 12 in Idaho and areas that
have experienced recent fire activity is a great concern into the
overnight hours on Tuesday and Wednesday morning.

The surface low pressure center will track northeast into western
Montana during the day Wednesday bringing much cooler temps and
rain, possibly mixed with snow at valley floors, especially
Wednesday morning. Moderate to heavy rain will likely create
widespread ponding and some rise to the smaller creeks and
streams. Mountains will likely see a heavy wet snow over the
mountain passes along the Continental Divide periodically creating
hazardous driving conditions. The low pressure will likely cut off
from the main upper level flow just east of Glacier National Park
wrapping moisture around the low into northwest Montana Wednesday
evening through Thursday. This region, including Marias Pass, will
likely be impacted the most with 12-24 hours of on and off snow.
Some snow could also spread even further west and impact lower
elevations such as West Glacier and the Kalispell area. Keep
apprised to possible forecast changes due to the complexity of
this system and the time we have until it occurs.


.AVIATION...Wind and Scattered showers will be diminishing rather
quickly this evening as drier, more stable air moves in from the
west. An upper level ridge of high pressure will be building into
northern Idaho and western Montana during the next 24 hours. This
ridge will provide dry, more favorable conditions for aviation
operations. The only caveat to this pattern will be the potential
for patchy morning fog Saturday morning across the Idaho Panhandle
and northwest Montana, including KGPI.




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