Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 110345
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
845 PM MST Sat Dec 10 2016

.DISCUSSION...Dense fog continues to be the main problem this
evening, and the dense fog advisory has been expanded to include
several more forecast zones. These include the Lower Treasure
Valley of Oregon, the Upper Weiser River Basin, and Baker County.
Fog is expected to continue well into tomorrow morning and it will
continue to be dense at times. Otherwise, as small area of showers
producing a wintry mix was moving east across much of Owyhee
County and southern portions of the Upper Treasure Valley as of
830 pm MST. These showers will move into the western Magic Valley
and southern Twin Falls County this evening. Precip amounts will
be light. Additional showers are expected in the higher terrain of
Baker County and in the west central and Boise mountains later
tonight. Again, precip amounts will be light. The only forecast
updates at this time were to add more dense fog.

&&

.AVIATION...Widespread LIFR/IFR conditions in the Upper and Lower
Treasure Valley, Weiser River Valley and Baker Valley through
about 18Z, though areas of fog will likely persist in the Upper
Treasure Valley through the afternoon. Elsewhere, low VFR/MVFR
conditions will prevail tonight and tomorrow. Isolated showers
continue in Idaho`s Upper Treasure and south to the NV border, but
are expected to end before 06Z. Light and variable surface winds
tonight, except winds out of the SW 10-15 kts in the Magic Valley.
Winds aloft near 10K FT MSL: W 20-30 kts, increasing to 30-40 by
21Z.

&&

.PREV DISCUSSION...
SHORT TERM...Pcpn decreased or ended in most areas earlier today
as a cold front sagged esewd through our CWA. Fog is the main
problem now. Dense fog has developed in the Upper Treasure Valley
and is slowly expanding into the Lower Treasure Valley of Idaho.
With only light winds winds in the forecast, we expect areas of
dense fog through the night and Sunday morning in the Idaho
Treasure Valley, with patchy fog in other valleys of our CWA. Fog
will probably form again Sunday night and Monday morning. The main
moisture fetch across our southern zones continues to shift slowly
south, but the more northern stream will continue to provide snow
showers across our northern zones through Monday. Temperatures
will be near normal through Monday.

LONG TERM...Monday night through Saturday. Monday night into
Tuesday morning the overall pattern will have an arctic upper low
on the eastern side of the divide, but a weaker low is expected to
peel off on the western side of this low and move into the PACNW.
This smaller low will tap into a milder and moist flow off central
California. As we transition into the warm sector of this low on
Tuesday, a warm front will move into the southern portion of our CWA
and become mostly stationary. Warmer air overrunning the cooler
air in the area will produce another round of snowfall. This
pattern will continue through at least Wednesday night. Models are
in good agreement of this pattern, however, how far north this
front stalls is where the most uncertainty lies, and thus, the
areal coverage of the snowfall. By Thursday, models indicate the
low off the coast will rotate in, and sweep a cold front through
the area that will also move the warmer air off to the east. Snow
showers may continue on Friday with the upper level trough
passage. By Friday evening, models continue to be in agreement of
a cold northerly flow developing. With the likelihood of existing
snow cover and this pattern, temperatures are quite cold during
the latter part of the extended and confidence continues to grow
in this scenario.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Dense Fog Advisory until 8 AM MST Sunday IDZ012-014-033.
OR...Dense Fog Advisory until 8 AM MST /7 AM PST/ Sunday ORZ062-064.

&&

$$

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DISCUSSION...SP
AVIATION.....AB
PREV SHORT TERM...LC
PREV LONG TERM....EP/DD



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