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fxus65 kboi 182055 
afdboi

Area forecast discussion
National Weather Service Boise Idaho
255 PM MDT Fri Oct 18 2019

Short term...tonight through Sunday...a fast moving low pressure
system will track through the Pacific northwest late tonight and
Saturday. This is a dynamic system with strong upper level winds
and cold air aloft that will bring a quick but intense period of
rain/snow. Precipitation will overspread the area from west to
east early Saturday morning in advance of the trough. By afternoon
expect development to be more convective, and with strong westerly
winds shower development will be favored along west-facing
ridgelines. This could produce some shadowing in north/S Mountain
valleys to include the Long Valley. There is enough lift and cold
air aloft to support a slight chance of afternoon thunderstorms as
well. The strong winds aloft (45-55kts at ~10kft msl) and
tightening surface pressure gradient will produce gusty surface
winds. The strongest winds will blow across the open rangeland of
southeast Oregon and portions of southwest Idaho, and thus have
issued the Wind Advisory for these areas. West facing slopes in
the central Idaho mountains will also see gusty winds accompanying
the snowfall. Snow levels will range from around 6500 feet along
the Nevada border to 4500-5500 feet across Baker County and the west-
central Idaho mountains late tonight and Saturday. Mountain
valleys will see accumulations through mid-day Saturday, but then
expect temperatures to warm above freezing, briefly
slowing/halting accumulations. Sites above 6000 feet in the
W-central and northern Boise Mountains will see the greatest
snowfall totals with this storm.



Precipitation begins to taper off Saturday evening as the low digs
southeastward. Valleys will dry out Saturday night as snow showers
continue in the mountains under northwest flow aloft. Weak warm
advection accompanying a building ridge will support shower
development on Sunday, though precipitation will be light and
likely focused across northern zones. High temperatures will run
below normal through the weekend.



Long term...Sunday night through Friday...unsettled northwest
flow persists through the period after a strong dynamic system
passes to the east on Monday. Temperatures will rebound a couple
degrees above normal on Tuesday as a high pressure center nudges
towards the Pacific coast. Snow showers are expected to linger
over the central Idaho mountains through Tuesday with snow levels
between 6000-7000 ft mean sea level. Another trough will drop to the east of
the intermountain west on Wednesday, reinforcing a dry northwest
flow over the County Warning Area through the extended. This will cause
temperatures to drop roughly 3-5 degrees below average.

&&

Aviation...VFR under mid-level ceilings causing mountain
obscuration. Isolated rain and snow showers tapering off after
18/21z. Snow levels: 5k-6k ft mean sea level. Surface winds: west-northwest 10-20 kts
with gusts up to 25 kts in the Magic Valley. Winds aloft at 10k ft
msl: west 20-30 kts.

Weekend outlook...widespread rain and snow Saturday with isolated
thunderstorm activity. Snow above 5000 feet mean sea level Saturday
afternoon, 4000 early Sunday morning. Widespread MVFR/IFR and
mountain obscuration. Strong surface winds across southeast or Saturday
afternoon with gusts up to 40 kts. Conditions improving Sunday to
generally VFR except for lingering rain/snow showers in the
central Idaho mountains. Winds aloft at 10kft msl: west to
northwest 40-60 kts Saturday, decreasing Sunday.

&&



Boi watches/warnings/advisories...
Idaho...Wind Advisory from noon to 8 PM MDT Saturday idz029.
Winter Weather Advisory from 6 am Saturday to midnight MDT
Saturday night idz011.
Or...Wind Advisory from noon MDT /11 am PDT/ to 8 PM MDT /7 PM PDT/
Saturday orz061-063.

&&

$$

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