Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 200257

Area Forecast Discussion
National Weather Service Boise ID
857 PM MDT Tue Sep 19 2017

.DISCUSSION...A lull in the shower activity this evening will be
temporary as widespread showers in northwest Oregon skirt across
mainly northern portions of SE Oregon and SW Idaho. Will update to
lower pops slightly this evening and remove isolated
thunderstorms. The showers will continue through Wednesday, mainly
across the northern high terrain. Snow accumulations 2-5 inches
are expected in the northern mountains mainly above 7000 feet.
Winds will increase on Wednesday, approaching advisory levels (30
mph and/or gusts 45 mph) in portions of SE Oregon by afternoon.


.AVIATION...VFR except local brief MVFR conditions in heavier
showers. Snow levels 7K-8K ft MSL. Isolated to scattered showers
tonight, becoming widespread Wednesday, then decreasing to
scattered Wednesday evening. Surface winds south to west 10-20 kts
increasing to 15-25 kts after 15z Wednesday and shifting to west
after 18z. Winds aloft at 10k ft msl west 40-50 kts.


SHORT TERM...Tonight through Thursday...Cool, wet, and unsettled
pattern continues with another surge of shower activity expected
overnight and through Wednesday, with higher terrain thunderstorms
again possible during the afternoon hours. An approaching trough
will advance a cold front into the area by Wednesday afternoon.
This approach will bring a very tight pressure gradient across the
area, bringing breezy wind across much of southeast Oregon and
into southwestern Idaho. Winds currently remain below thresholds
for highlights, but models continue to bump them up with each run
so the threat continues to be evaluated. Passage of the front on
Wednesday afternoon will end the threat of thunderstorm activity
and help to relax wind across the area. As the trough digs across
the forecast area on Thursday, expect cooling temperatures with
high temperatures 15 to 20 degrees below normal. Additionally,
there will be enough lingering moisture to keep shower activity
possible across much of the forecast area.

LONG TERM...Thursday night through Tuesday...A closed upper level
low will be in the midst of traversing the region Thursday night,
bringing low elevation rain and mountain snow across the region.
Snow levels will come down to about 5200 ft MSL along the northern
zones and about 5800 ft MSL along the southern zones at this
time. These snow levels may be low enough to see a rain-snow mix
along the Long Valley early Friday morning. Snow levels will rise
slowly under a northwesterly flow aloft as precipitation continues
to fall across the region most of the day Friday, decreasing west
to east as the upper low moves out of the region. By Saturday
afternoon, lingering showers will be focused across the west
central Idaho mountains and south towards the Nevada border. An
upper high will build into the Pacific Northwest in the low`s
wake, for a drying and warming trend across the region. Maximum
temperatures will be about 15 below normal at the start of the
extended forecast, gradually increasing a few degrees each day,
ending Tuesday within 5 degrees of normal.





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