Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 201001

Area Forecast Discussion
National Weather Service Boise ID
401 AM MDT Fri Oct 20 2017

.SHORT TERM...Today through Saturday...A sharp cold front working
across the region this morning will be accompanied by rain, high
elevation snow and gusty winds. The front will push through the
Lower Treasure Valley by 5AM reaching the Western Magic Valley by
8AM. Snow levels will drop from 8000 feet ahead of the front to
around 5000 feet by this afternoon. Expect accumulations of less
than an inch in mountain valleys below 6000 feet with 2-5 inches
at sites above 6000 feet. Gusty west winds with the frontal
passage will reach 45 mph, with windy conditions continuing
through this afternoon as flow aloft mixes to the surface. Though
the probability is low, instability and dynamics aloft could
support a low-topped thunderstorm this afternoon. Graupel showers
at lower elevations are also a possibility. Showers linger in the
ID mountains well into this evening as southeast Oregon and Snake
Plain dry out. The next system is quick to follow with a warm
front pushing into southeast Oregon Saturday morning where
precipitation will start as snow or rain/snow mix for all but the
lowest elevations in Malheur county. Sites down to 4000 feet will
see accumulating snow (up to 2 inches) before it changes to rain
in the late morning. The warm front and accompanying precipitation
pushes into southwest Idaho during the day. Snow levels will rise
to around 5000 feet in the central ID mountains to around 6000
feet along the ID/NV border. Winds will shift to the south-
southeast behind the warm front.

.LONG TERM...Saturday night through Thursday...Moist zonal flow
will keep precipitation going across the west central Idaho
mountains and NE Oregon mountains through Monday morning, with
generally dry conditions across the the Snake River basin and
areas south. An upper level ridge expands across the West on
Monday and Tuesday, bringing warmer temperatures (around 5-7
degrees above normal). The ridge is short lived, as a system with
a potent cold front moves southeast along the Canadian Rockies
into Montana late Wednesday into Thursday. Temperatures will cool
on Thursday with this system, although forecast confidence is low
with the differences in the positioning of the cold front.


.AVIATION...Conditions deteriorating to low VFR to MVFR and local
IFR this morning as widespread precipitation spreads across SE
Oregon and SW Idaho along a cold front. Mountains will become
obscured. Snow levels lowering to 4500-5000ft. Behind the front,
precipitation will become showery in nature, and be focused on the
higher terrain, through this evening. Gusty surface winds up to
35kt possible with the frontal passage, becoming NW 15-25kt during
the afternoon with gusts to 35kt near KTWF KJER. Winds aloft at
10kft MSL: SW 35-50kt shifting to NW 20-30kt behind the front.

Weekend Outlook...Snow will spread across SE Oregon on Saturday
morning before changing to rain. Snow levels start at 3500-4000ft in
the morning, rising to 7500-9000ft by Saturday night. Expect
widespread precipitation on Saturday with mountain obscuration
continuing into Sunday. Surface winds will be SW-SE 10-20kt.





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