Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 241002
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
402 AM MDT Thu Apr 24 2014

.DISCUSSION...A push of moisture and instability are working their
way across central Washington/Oregon this morning. Many weather
stations under its path are showing fairly continuous light to
moderate rainfall with high mountain snow falling and the radar/
satellite trends support numerical model data which show this
activity over central Idaho and western Montana today where it
will produce a similar spread of precipitation. Heaviest amounts
can be expected over the complex terrain in central Idaho and
along the Idaho/Montana border as well as across much of NW
Montana, all locations which are highly favored for enhanced up-
slope precipitation in westerly flow aloft. Model instability
parameters suggest a progressively growing chance for
thunderstorms throughout the afternoon. However there are many
negating factors (cold surface temps, lack of sunshine, little
upper level jet support) which will limit the potential to, at
best, a slight chance of a thunderstorm or two.

Tonight the flow begins to take more of a southerly orientation
which will effectively reduce the chances for precipitation across
northwest Montana while maintaining chances over central Idaho
across in west central Montana (including Missoula/Bitterroot
Valley). Models are all showing a disturbance ejecting through the
flow on Friday which could produce some heavier rain showers and
perhaps a slight chance for a few lightning strikes Friday
afternoon over central/southwest Montana.

Saturday through Monday...A broad, cool trough of low pressure
will reside over the Northern Rockies region and provide us with
a moist, unstable environment. The best chance of significant
precipitation will occur Friday night and Saturday as a mid-level
circulation migrates northward through Montana and into Canada.
The upper trough will linger across the region Sunday, before
shifting east of the Continental Divide during the day Monday. The
atmosphere will be cool enough for snow in the mountains and
potentially some wet snow (or rain/snow mix) in the valleys of
western Montana during the night and early morning hours. Little,
if any, appreciable accumulations of snow are expected in the
valleys except for maybe grassy areas. However, mountain passes
will likely see some minor accumulations on road surface during
the night and morning hours making driving conditions a little
slick. Showers will be tapering off later Monday as a ridge of
high pressure nudges in from the west.

Tuesday through Wednesday...Medium range models continue to
develop a large scale ridge of high pressure centered either
along the West Coast or over the Pacific Northwest. Idaho and
western Montana will be on the eastern edge of this ridge feature
with some degree of a northerly flow over our region. Warmer and
drier weather is still in the forecast, but will wait to see if
the ridge axis shifts further east to help bolster confidence for
a warm, dry forecast.

&&

.AVIATION...Rain showers will become more numerous throughout the
day, especially near KMSO and KGPI where ceilings will be lowest
and visibility may at times be hampered. Gusty winds will once
again develop this afternoon, being strongest near showers. Winds
and precipitation will begin to subside around sunset.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

$$

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