Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 211645
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
945 AM MST Sat Jan 21 2017

.DISCUSSION...A weakening upper low off the Washington coast is
producing some showers across the area. In the Treasure valley,
these showers have been a mixture of rain, very wet snow, and
sleet. As of 0930, radar indicated much of the Snake River Valley,
from Mountain Home to Weiser is experiencing this mix of
precipitation. After this round, showers are expected to be
isolated in nature and confined mostly to the mountains for the
remainder of the day. The current forecast reflects this well. The
forecast was updated to remove fog in the Burns, OR valley, as
high level cloud cover improved visibilities.

&&

.AVIATION...Areas of light snow will produce IFR conditions mostly
across southwest Idaho today. Snake Plain will see the snow/IFR this
morning, while periods of snow will persist in the southwest Idaho
mountains through the day. Will see low VFR and isolated MVFR
otherwise. Surface winds 5-15 kts. West winds aloft of 15-20
kts at 10k feet msl.

Tonight and Sunday...Most areas dry overnight with isolated
MVFR/IFR in fog or low stratus developing. Next round of snow
develops across southeast Oregon early Sunday morning and southwest
Idaho by late Sunday morning bringing IFR conditions and obscuring
mountains.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Sunday...An upper trough, which
extends from a low centered off the Washington coast, will weaken
and lift to the north today. Scattered showers will continue
across SE Oregon and SW Idaho through the day, with rain/snow
showers in the lower valleys and snow showers in the higher
elevations. Precip amounts will be light. A second and stronger
low pressure system will approach the PacNW coast and stall
offshore on Sunday. A moist Southwesterly flow will spread light
to moderate precipitation into the area. Snow levels will be near
valley floors in the morning then rise to around 3000 feet in the
afternoon. Strong mid-level winds will create a drying downslope
affect off the Owyhees which will reduce precip totals for the
Upper Treasure Valley (less than an tenth of an inch). Greater
amounts are expected in the Lower Treasure Valley. Moderate
snowfall amounts are expected in a corridor stretching from
northern Malhuer County into Baker County and the Upper Weiser
Basin, although confidence is too low to warrant a Winter Weather
Advisory at this time. A deep surface low off the PacNW coast will
induce a strong pressure gradient for breezy SE winds by Sunday
afternoon. The strongest winds are expected in the Upper Treasure
Valley where winds will approach advisory levels.

LONG TERM...Sunday night through Friday...Precipitation will
remain over the forecast area Sunday night and Monday as a warm
front moves north over the forecast area Sunday night, then a cold
front moves over the area on Monday. Snow levels will rising to
around 3500 feet Sunday night, but will fall back to valley floors
behind the cold front. Precipitation will decrease over the area
Monday night and Tuesday as a weakening upper level low moves east
over the forecast area. A ridge of high pressure begins to build
over the area Wednesday and will remain through the end of the
week. This ridge will bring a cold northerly flow to the region
with below normal temperatures for the end of the week. Also, as
the ridge builds will see the valley inversions strengthen.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...None.

&&

$$

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DISCUSSION...EP
AVIATION.....DG
PREV SHORT TERM...BW
PREV LONG TERM....JA


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