Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 121009
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
309 AM MST Tue Dec 12 2017

.SHORT TERM...Today through Wednesday...Inversion continues as the
upper ridge shifts slightly westward through Wednesday. A weak
feature moving over the ridge will increase mid-high level
moisture tonight into Wednesday, bringing clouds to areas that
have remained clear of the recent stratus. Expect little change
in the day-to-day evolution of low stratus and fog through
Wednesday, with daytime clearing across the central Snake Plain
and areas of Baker and Harney county. And areas that clear will
see locally dense fog redevelop this evening. Have added flurries
to the forecast for areas under the stratus, otherwise area
remains dry. For temperatures, kept close to persistence today
with valley sites seeing below normal high temperatures to above
normal in the mountains. It`s slightly cooler in the mountains
Wednesday as the upper ridge axis slips eastward, but don`t expect
much change in the valleys.

.LONG TERM...Wednesday night through Monday...Persistent
stratus/fog is expected to continue Thursday as the upper ridge
axis remains over the Pacific Northwest. temperatures across the
lower valleys expected to remain below normal once again.

Changes finally expected late Friday afternoon and evening as the
upper ridge erodes as a weak front pushes through the region. The
inversion should finally break but it will take a majority of the
day as winds expected to remain light and dont increase until the
evening. As a result, a wintry mix is possible across the lower
elevations and snow in the mountains. The lowest elevations
(generally along the Snake River and Lower Treasure valley), could
see pockets of freezing drizzle Friday afternoon prior to the
inversion scouring/mixing out. For the remainder of the weekend,
extended models differ slightly on the timing of the warm air
advection and thus precipitation moving into the Pacific
Northwest. Potential brief break Saturday before the warm front
moves through the Pacific Northwest and Idaho Panhandle Sunday and
Monday. At this time, the best chance for precipitation should be
across the northern portions of the forecast area. Temperatures
finally rebound after Friday to just above normal.

&&

.AVIATION...Stratus/fog in the lower valleys causing MVFR/IFR
conditions. Repeat of stratus/fog for Wednesday morning. Surface
winds light and variable. Winds aloft at 10 KFT MSL variable 5-15
kts.

&&

.AIR STAGNATION...Inversion is in play through the end of the
week. See little change in mixing heights or winds in the mixed
layer through Friday. A weak system moving through the area late
Friday will be the best chance to break the inversion, though not
confident that it will scour out in the lowest valleys (sites
below 3k feet MSL).

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Dense Fog Advisory until 11 AM MST this morning IDZ016.
OR...None.

&&

$$

www.weather.gov/Boise
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SHORT TERM...DG
LONG TERM....CR
AVIATION.....CR
AIR STAGNATION...DG



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