Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 100346
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
846 PM MST Fri Dec 9 2016

.DISCUSSION...Freezing rain has been much slower to end than
previously expected as the low level cold air refuses to budge
from northwest Ada County and the Lower Treasure Valley. Issued a
winter weather advisory for freezing rain for the Upper Treasure
Valley - valid until 12Z. This may need to be extended to later in
the morning, but will give it time to see if the warm air aloft
finally wins out. We made significant changes to the minimum
temperatures overnight, lowering them for the advisory areas.
Otherwise, we still expect moderate snowfall in the mountains
tonight and the advisories there were left as they were. The moist
flow shows no indication of slackening up tonight and qpf amounts
will be higher than we typically get. Freezing rain accumulations
on trees and power lines may be a problem overnight. If some of
the models indicating much higher qpf (up to 0.75 in the valleys
overnight) than we have currently forecast were to verify, we`d
be well into ice storm warning criteria. However, at this time, we
do not believe they will. We have already issued new zones and
sent new products to the web, so all updates have been completed.

&&

.AVIATION...MVFR/IFR conditions in mountain snow and valley
freezing rain this evening. At KEUL and KBOI, temperatures are now
expected to remain around freezing and will likely remain that way
through Saturday morning. Mountain snow will continue across the
Central Mountains of Idaho through Saturday. Surface winds will be
light and variable at most locations. Winds aloft around 10 kft
will be westerly at 25 to 30 kts.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Sunday...Temperatures across the
area continue to slowly increase as precipitation is ongoing with
the moist zonal flow and warm front that is working its way
northeast. In the Snake River Valley, snow has turn to rain in
the Western Magic Valley up through the Mountain Home area. Boise
area has seen a wintry mix through the day, but the next round of
showers later this afternoon will likely be rain. The Lower
Treasure Valley is still cold enough for snow. Elsewhere, snow is
expected to be ongoing, especially in the West-Central Idaho
Mountains. Winter Weather Advisories are in effect to highlight
this snowfall through Saturday morning. On Saturday afternoon, a
shortwave trough will move across the Idaho Panhandle and a weak
frontal boundary is expected to move through from NW to SE and
bring a brief break in precip. Another shortwave will move onshore
Sunday and bring another round of precip to mainly the northern
half of the CWA.

LONG TERM...Sunday night through Friday...An active weather
pattern will continue through Tuesday with a chance of snow at
times. The upper level pattern will remain in a moist zonal flow
with strong westerly winds aloft. This pattern will keep snow
falling in the mountains through the period with orographic
enhancement helping boost snow accumulations in the highest
elevations. Valley locations across southwestern Idaho and
southeastern Oregon will likely have some light snow, on and off
again, during this period as well. However, the lowest valleys
will also warm to just above freezing during the afternoon hours
each day and rain may mix with the snow at times.

Wednesday through Friday Night...Model analysis demonstrating a
colder, drier solution than compared to the last couple runs.
Trended current forecast towards the GFS, though current forecast is
a bit wetter than this preferred model suggests. Will leave this
slight inconsistency in hopes of achieving additional model run
agreement. Overall, it appears that a dry, arctic airmass will
protrude over the area and present limited moisture. An area of low
pressure will advance towards the California coast late Friday,
which will push some moisture northeast, reaching into the area by
early Saturday morning.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory until 5 AM MST Saturday IDZ012-014-033.
     Winter Weather Advisory until 11 AM MST Saturday IDZ011-013-028.
OR...Winter Weather Advisory until 5 AM MST /4 AM PST/ Saturday
     ORZ062-064.

&&

$$

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DISCUSSION...SP
AVIATION.....JS
PREV SHORT TERM...EP
PREV LONG TERM....JB/KB


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