915
FXUS65 KBOI 110936
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
236 AM MST Thu Dec 11 2025

.SHORT TERM...Today through Saturday night...Continued warm and
dry several more days under a broad long wave upper ridge anchored
over the eastern Pacific and western US. The atmospheric river in
the north Pacific has shifted north and now comes inland across
WA and northern ID. A surface inversion, along with light winds,
has created air stagnation in the valleys that will continue
through at least Sunday night. High temps will continue 15 to
20 degrees above normal, but not quite as warm as yesterday.
Low temps should get gradually colder in the valleys as the
inversion persists, but not as cold as it would be with snow
cover. We should also have less valley fog than Wednesday
morning as the air mass continues to slowly dry out.

.LONG TERM...Sunday through Thursday...Above normal temperatures
with clearing skies will continue air stagnation concerns as high
pressure remains over the Intermountain West through Monday. The
ridge axis will gradually move east on Sunday, bringing a slight
reduction in temperatures and an increase in clouds as a weak low
skirts to our south over southern Nevada. This low will bring a
slight uptick in westerly winds, but likely won`t bring enough
mixing to clear out any lingering low clouds or stagnant air in
sheltered valleys. That pattern shift looks to come on Tuesday
with another atmospheric river. This plume of moisture is poised
to move into the Pacific Northwest on Tuesday, bringing high
terrain showers primarily in southeast Oregon and central Idaho.
Snow levels will likely remain elevated around 7000-8500 feet
MSL thanks to warm southwest flow initially, but could lower
back to 5000-6000 feet MSL by Wednesday. There is slight
disagreement among long range models in the strength of the
Pacific High, with some ensemble solutions showing the ridge
maintaining strength over the region and keeping showers to the
north and west of southeast Oregon and southwest Idaho Tuesday
through Thursday.

With some lingering uncertainty in the evolution of the pattern,
current forecast chances for any significant accumulation of rain
or snow are minimal over our region. Temperatures look to remain
around 10-20 degrees above normal through the long term period
with later weekdays showing the best potential for significant
cooling.

&&

.AVIATION...Mainly VFR with high clouds overnight. However,
patchy fog will develop in the early morning across sheltered
valleys of SE Oregon and SW Idaho. Highest chance of fog is near
KBKE/KONO/KMYL. Scattered light showers returning to the west-
central Idaho mountains Thursday, with MVFR/IFR conditions and
mountain obscuration in precipitation. Snow levels 7500-8500 ft
MSL. Surface winds: W-SE 5-15 kt. Winds aloft at 10kft MSL:
W-NW 25-40 kt.

KBOI...VFR expected with fog/stratus unlikely (less than 10%
chance) through Thursday morning. Surface winds: SE less than
10 kt, becoming NW 4-8 kt Thursday afternoon.

Weekend Outlook...Mostly VFR with low confidence in low stratus
and fog in sheltered valleys each morning. Winds will generally
be from W-SW less than 10 kt.

&&

.AIR STAGNATION...A broad upper-level ridge will continue, with
mixing heights lowering to 1,500 to 2,500 feet AGL today and to
1,000 to 2,000 feet AGL Friday through Sunday. At the same time,
winds are expected to be less than 10 mph resulting in sustained
poor ventilation. An Air Stagnation Advisory will remain in
effect Friday through Sunday. A system early next week may
provide increased mixing and winds, ending the air stagnation,
with an active pattern expected beyond.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Air Stagnation Advisory from 5 AM Friday to 5 AM MST Monday
     IDZ012-014-016-033.
OR...Air Stagnation Advisory from 5 AM MST /4 AM PST/ Friday to 5
     AM MST /4 AM PST/ Monday ORZ061>064.

&&

$$

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SHORT TERM...LC
LONG TERM....SA
AVIATION.....SA
AIR STAGNATION...LC