Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 162023
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
223 PM MDT Wed Apr 16 2014

...More snow over the mountain passes late Thursday night/Friday...
...Gusty west winds Friday across western Montana/Lemhi County...

.DISCUSSION...
Tonight...There is enough Pacific moisture caught up in a
northwesterly flow aloft to keep clouds and scattered showers
across much of northern Idaho and western Montana through the
evening hours. Showers will be tapering off after nightfall with
the exception of the northwest Montana mountains.

Thursday...A low amplitude ridge of high pressure will serve as
some limited protection from the influx of moisture coming in off
the Pacific ocean. We still expect plenty of clouds, but any
chances of precipitation will be confined to the Idaho Panhandle
and northwest Montana. High temperatures in the valleys will range
from the low 60s across north-central Idaho to mid 50s in
northwest Montana.


Thursday night...A vigorous frontal system will be passing through
the Northern Rockies region overnight. This system possesses
considerable moisture and strong dynamics. We will see snow levels
lower quickly after midnight with accumulating snow impacting the
mountain passes along the Idaho/Montana border, as well as Marias
Pass. Road conditions may become difficult towards morning as
temperatures cool and snow begins to stick to road surfaces.
Precipitation in the valleys should remain mostly as rain. Some of
the heaviest rainfall will occur over the Idaho Panhandle and
adjacent mountains on the Montana side. Heavier rainfall could
result in some loose debris (rocks/soil) spilling onto roadways in
those lower valleys in western Idaho county.

Friday...Strong westerly winds aloft combined with a supportive
surface pressure gradient will promote windy conditions across
western Montana and Lemhi county during the day. Choppy surface
water conditions on area lakes will likely start up right away in
the morning and continue throughout the day. However, winds are
not expected to be very gusty across western Clearwater and Idaho
counties in north-central Idaho. Mountain snow showers can be
expected, but any additional snow will likely melt as it falls on
the roadways by mid-morning for minimal impact.

Friday Night...Both wind and shower activity will be diminishing
quickly during the evening hours in response to higher pressure
building in from the west. If there is enough clearing
overnight, valley fog may become an issue with temperatures
cooling well into the 20s at many locations. Lower valleys across
Clearwater and Idaho counties will remain in the 30s to near 40
degrees however.

All markers point towards a very pleasant Easter weekend with
Saturday likely a touch warmer than Sunday. However periods of
sunshine will be limited both days with moisture still finding its
way through the weak high pressure ridge. Some afternoon showers
are possible late in the day across NW and SW Montana on Sunday
with shower activity becoming more widespread and stronger Monday
and Tuesday afternoon. In fact the steepening southwesterly flow
aloft will lend to a progressively better chance for thunderstorms
each day.

By Wednesday, the longer range models are showing a stronger
weather system ejecting out of the Desert Southwest/Great Basin
Regions and into the Northern Rockies. A quick analysis of prior
systems with similar trajectory and origin reveals the potential
for a wide variety of impacts attributed to heavy precipitation.
At this time, confidence is higher than normal that we`ll see a
strong weather system with abundant precipitation. However, there
remains lower confidence in the thermal profile which will
ultimately dictate if those impacts are related to excess rainfall
(i.e. flooding, mud/rock slides & debris flows), heavy snowfall
(impacting travel over mountain passes, back country and higher
elevation valleys) or a culmination of the two. Stay tuned as we
sort out these details over the next few days.


&&

.AVIATION...Variable mid to high level cloud cover will help keep
winds at bay today with only a few brief hours of breezy
conditions possible this afternoon at KMSO, KGPI and KBTM. But any
wind will subside shortly after 17/0200z this evening. Otherwise
expect similar cloudiness to persist throughout the night and into
tomorrow in advance of a stronger weather system expected into the
region tomorrow night through Friday.

&&

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

$$

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