Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 180324
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
824 PM MST Tue Jan 17 2017

.DISCUSSION...Observed winds across Baker county increased more
than anticipated this evening, resulting in an earlier update to
increase wind through the evening. Additionally, the slower
arrival of cloud cover for portions of the area left the need for
lowered minimum temperatures, mainly impacting Treasure Valley.
The challenge remains on details surrounding the upcoming winter
storm with regards to warming, snow amounts, and presence of
freezing rain. A few tweaks were made to current forecast, but
nothing significant in regards to current highlights.

&&

.AVIATION...Mostly VFR this evening with areas of MVFR haze in
the Snake River Plain from KONO-KMUO. Otherwise, increasing and
lowering clouds from the west ahead of an approaching Pacific
storm system. Precipitation, mainly as snow, will move into
southeast Oregon around 09Z and southwest Idaho around 15Z. May
see areas of freezing rain along the Nevada border Wednesday. Once
the snow begins to fall, will see widespread IFR and areas of LIFR
conditions along with mountain obscuration. Surface winds
generally east to south 12 knots or less, except easterly 20-30
knots at KJER and KBKE. Winds aloft southwesterly 15-25 knots.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Thursday...Very complex weather
coming the next few days. Snow will begin in southeast Oregon from
west to east late tonight and spread into southwest Idaho early
Wednesday morning. Latest thinking is that precip will remain all
snow for virtually the entire area through tomorrow afternoon.
Snow levels will rise, however, and snow will mix with, or change
to, rain or freezing rain, depending on where you are. Best
chances for heavy snow through Thursday are: northern Malheur,
Baker, Adams, Washington, and northeastern Harney counties, and
the mountains above around 6000 feet. The Lower Treasure Valley
will see plenty of snow, but may also change to or mix with
freezing rain from Wednesday evening into early Thursday. Snow
depth will depend directly on how much of the precip falls as
freezing rain. The Upper Treasure Valley is an area of low
confidence. Some models indicate all snow, others mostly rain. We
have decided that all snow for Thursday makes the most sense,
while mixing with or changing to freezing rain or even rain in
some areas Wednesday night was the best bet. This is extremely
elevation dependent, as the northern portion of the valley has the
best chance for snow, while the southern part the best chance to
change over or mix. We no longer see the snow levels getting as
high as we previously thought. Winter Storm warnings and
advisories have been updated with this thinking in mind. Please
see the winter weather products for snow/ice amounts. Please also
stay aware of updates as this forecast will be in flux right up
until the event. The system moves out Thursday, just in time to
allow the next one to move in at the beginning of the long term
period.

LONG TERM...Thursday night through Tuesday...Active period
expected for the extended with two systems moving through the
region. Will see lingering showers from the previous system move
out late Thursday night ahead of a short break in precipitation
overnight. Next system drops out of the northern Pacific bringing
precipitation across the region by mid-day Friday. Precipitation
will fall mainly as snow during this event. Most of the energy
associated with this system will dip to the south of the region,
so snow totals will generally be light. Short dry spell Saturday
night ahead of a second system pushing in Sunday. By Tuesday,
heights will slowly rise as a ridge begins to build over the
Pacific Northwest and showers begin to taper off. Temperatures
will be about 5-10 degrees below normal for the duration of the
forecast.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Winter Storm Warning from 11 AM Wednesday to 5 PM MST Thursday
     IDZ016.
     Winter Storm Warning from 5 AM Wednesday to 11 AM MST Thursday
     IDZ011-012-033.
     Winter Weather Advisory from 11 AM Wednesday to 5 PM MST
     Thursday IDZ015-028-030.
     Winter Weather Advisory from 5 AM Wednesday to 11 AM MST
     Thursday IDZ013-014-029.
OR...Winter Storm Warning from 5 AM MST /4 AM PST/ Wednesday to 11 AM
     MST /10 AM PST/ Thursday ORZ062>064.
     Winter Weather Advisory until 4 AM PST Thursday ORZ061.

&&

$$

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DISCUSSION...KB
AVIATION.....JA
PREV SHORT TERM...SP
PREV LONG TERM....AB/WH



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