Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 180354
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
854 PM MST Wed Jan 17 2018

.DISCUSSION...Quiet conditions seen across the area tonight, with
some occasional gusts of wind. Patchy fog remains possible for
sheltered locations tonight, ahead of the approaching cold front.
Timing and intensity still look on track - activity looks to move
into eastern Oregon Thursday morning, and spread east through the
day. Some question remains about potential shadowing for the
Treasure Valley, but current forecast remains representative. No
changes needed so far this evening.

&&

.AVIATION...VFR with increasing clouds. Then, MVFR/IFR due to rain
and snow beginning from NW to SE after 18/16Z. Surface winds
generally SSE around 10 kts, with gusts to 25 kts after 18/18Z.
Winds aloft near 10 KFT MSL: SW 40-5 kts.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Friday...An upper ridge will shift
east tonight, followed by increasing southwest flow aloft on
Thursday. Precipitation along and ahead of a cold front will
spread into southeast Oregon and central Idaho on Thursday. Warmer
air ahead of the front will lead to high snow levels, ranging
from 7000 to 8500 feet. The front will continue to push through
the area Thursday night, accompanied by widespread precipitation
and falling snow levels. Additional light snow accumulations are
likely overnight, mainly above 4500 feet. An upper trough will
follow the cold front on Friday. Snow levels will lower to near
valley floors, with a chance of rain and snow showers in the lower
valleys and snow showers (with light accumulations) in the higher
elevations. Breezy to locally windy conditions will develop
through Thursday afternoon as the front approaches, with the
strongest winds expected in the mountains and near the OR/NV
border. Winds are not expected to be strong with the frontal
passage. Record and near record temperatures are forecast for
Thursday. Temperatures will be much cooler on Friday (near or
slightly above normal).

LONG TERM...Friday night through Wednesday...The long term
forecast continues to be very active. The exiting trough Friday
night is followed closely by another trough early Saturday
morning. Snow levels sit right around valley floors at the
beginning of the period. QPF amounts on Saturday are not very
impressive with little to no accumulations in the lower valleys.
So even with the snow levels down to the valley floors, snow
accumulations for the valley on Saturday will be little to none.
There will be a brief break in the precipitation Sunday morning
before the next trough pushes in. Lower valleys are likely to see
this system begin as snow then changeover to a wintry mix or
straight rain. This pattern will continue through Tuesday evening
with each new trough bringing chances of snow to lower valleys,
but quickly transitioning to a wintry mix then rain. Snow levels
creep up above 3500 feet MSL by late Wednesday which will turn any
precipitation in the lower valleys to rain. Temperatures hover
right around seasonal norms.

&&

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

&&

$$

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DISCUSSION...KB
AVIATION.....EP
PREV SHORT TERM...BW
PREV LONG TERM....JC/JC



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