Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 172320 CCA
AFDBOI

Area Forecast Discussion...Corrected to Add Hydrology
National Weather Service Boise ID
355 PM MST Tue Jan 17 2017

.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.

&&

.AVIATION...Lingering areas of MVFR conditions in haze in the
Treasure Valley west of KBOI. Increasing clouds from the northwest
with the incoming Pacific system. Precip will begin over SE Oregon
after 18/06Z and southwest Idaho after 18/12Z. Precip will begin
as snow but will see areas of snow and freezing rain along the
Nevada border Wednesday and in the Treasure Valley Wednesday
evening and night. Widespread IFR and areas of LIFR conditions in
snow along with mountain obscuration will spread over the region.
Surface winds: mainly east-southeast 5-15 kts, except 15-15 kts in
KJER and KBKE. Winds aloft near 10kft MSL: WSW 10-20 kts,
increasing to 25-40 kts kts after 18/03Z.

.HYDROLOGY...Wednesday night and Thursday, rain and snowmelt on
frozen ground may result in standing water on city streets,
highways, county roads, and other low-lying areas in the Upper
Treasure Valley and portions of the Lower Treasure Valley on the
Idaho side. Areas where snow and ice have clogged street gutters,
storm drains, and ditches will be the most susceptible. Water levels
in small creeks and streams may be elevated as well.

Ice continues to cover much of the Snake River from around Ontario
and Payette downstream to near Weiser. Water levels along this reach
of the Snake River have trended down the past few days. However,
weather conditions through mid-week will increase the potential for
ice jams and fluctuating water levels. Folks in low-lying areas near
the Snake River, especially around Ontario and Payette should
monitor river conditions and be prepared for fluctuating river
levels and possible lowland flooding due to ice jams.

&&

.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 from 10 PM this evening to 4 AM PST
     Thursday ORZ061.

&&

$$

www.weather.gov/Boise
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www.twitter.com/NWSBoise

SHORT TERM...SP
LONG TERM....AB/WH
AVIATION.....AB
HYDROLOGY....TL



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