Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 230346
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
846 PM MST Wed Feb 22 2017

.DISCUSSION...Impressive tightly-wound low pressure system
centered near Twin Falls will be the focus for locally moderate to
heavy snow showers through Thursday evening. The snowfall amounts
and locations of heaviest snow will be difficult to forecast since
the amounts will be determined by the track of the system. Latest
model runs support our current Winter Weather Advisories and
Warning, although the amounts may vary significantly over a short
distance. The low pressure system is expected to shift only very
slightly to the northeast tonight, and meander over Eastern Idaho
through Thursday night before gradually weakening on Friday. No
updates for now.

The Flood Warning for the Weiser River near Weiser was cancelled
as the river level receded below flood stage earlier this evening.
Minor flooding will continue on the Malheur River near Vale
through tonight and recede below flood stage early Thursday
morning.

&&

.AVIATION...Generally low VFR, except for MVFR-IFR in snow east
of a line from KREO-KMYL. Snow will generally taper off Friday
morning, except in central ID mountains and Magic Valley.
Mountains obscured. Winds aloft at 10kft MSL: NW-NE 20-35kt.
Surface winds generally W-NW 5-15kt becoming W-NW 15-25kt Thu
afternoon, gusts to 35kt in Baker, Treasure and Magic Valleys
during the afternoon.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Friday...A Pacific storm system,
currently located near the Idaho-Oregon-Nevada border, is set to
continue its journey east, sliding along the Nevada border where
the main focus for snowfall will be. This system will stall over
eastern Idaho, allowing wrap-around moisture to work into the area
for an extended snow event over portions of south central Idaho.
The Southwest Highlands and portions of the western Magic Valley
are under a Winter Weather Advisory while southern Twin Falls
County is under a Winter Storm Warning. See products for more
detail. The Lower Treasure Valley is expected to remain dry
through the period, as will portions of the western Canyon and Ada
Counties. Elsewhere, will see light snowfall totals. Most
precipitation will fall as snow with a mix of rain and snow at the
lower elevations. Behind this system, winds will pick up from the
northwest to 20 to 30 mph tonight, diminishing tomorrow around
sunset. Much drier and cooler Friday as the upper level flow turns
south and west.

Cooler temperatures today will begin to bring hydrology related
concerns down a notch. Still have Flood Warnings out for both
Weiser River at Weiser and Malheur River at Vale, but both river
have either crested or are near crest and will be receding with
cooling temperatures.

LONG TERM...Friday night through Tuesday...Remnant moisture
around the area will leave some isolated to scattered activity
across the forecast area Friday night. During this time, an area
of low pressure will move south along the Pacific coast, pushing
flow more southwesterly as it advances. Models diverge fairly
quickly into the forecast period, with debate continuing on the
whether the area of low pressure stays closed or opens to become a
wave. The majority of numerical models have it turning into a
wave by the time it reaches the Oregon/California border on
Saturday afternoon. This system will scoot over the desert
southwest on Sunday, bringing an increased northwesterly flow
across the forecast area as it moves east.

Also on Sunday, leftovers of area of low pressure will move into
the Pacific northwest, with the axis of the trough beginning to
move more inland by Sunday morning. This system will continue to
dive south, with its axis approaching the forecast area Sunday
afternoon. By this time, precipitation associated with this system
will be widespread, though temperatures continue to be a slight
question, keeping the precipitation type a challenge to forecast.
The trough axis will move slowly through the area through Monday
evening with another push of moisture coming on its heels. This
next push is disputed among models, but confidence in the more
widespread precipitation for Monday is increasing. Unsettled
weather remains through Tuesday.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory until 11 PM MST Thursday IDZ016.
     Winter Storm Warning until 11 PM MST Thursday IDZ030.
     Winter Weather Advisory until 11 AM MST Thursday IDZ015.
OR...None.

&&

$$

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DISCUSSION...BW
AVIATION.....KA
PREV SHORT TERM...AB
PREV LONG TERM....KB/WH



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