203
FXUS65 KBOI 221617
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
917 AM MST Sat Nov 22 2025

.DISCUSSION...Many valley areas waking up to low stratus and
areas of fog this morning. Satellite imagery indicates these
conditions are widespread across most of the region, and
observations are showing dense fog in portions of Baker County,
the lower Treasure Valley of Oregon, and the Magic Valley. High
pressure remains in control overhead, with a series of troughs
to the west over the Pacific. The ridge of high pressure will
keep inversion conditions in place today into Sunday, with
guidance suggesting mixing from the surface up to 2500-3000 feet
above ground level. This should allow for most locations to
eventually mix out low level stratus by the afternoon, but will
likely mean a return overnight (70% chance for Lower Treasure
Valley of Oregon). Dense Fog Advisory in effect through 9am
PT/10am MT for Baker Valley and the Magic Valley. Expect
improving conditions through the day. The current forecast
handles the situation well with no further updates planned this
morning.

&&

.AVIATION...Areas of LIFR-MVFR this morning in fog/low stratus.
Conditions improving to VFR around 17-18z. Surface winds: S-E 5-10
kt. Winds aloft at 10kft MSL: S-W 5-15 kt.

KBOI...VFR under mostly sunny skies. Surface winds: SE 5-10 kt.

Sunday Outlook...Areas of valley fog/low stratus Sunday morning with
improvement in the afternoon. A cold front late Sunday will bring
light precipitation mainly to northern areas and mountain
obscuration. Snow levels 5500-6500 ft MSL Sunday evening, falling to
3000-4500 ft MSL by Monday morning. Surface winds: SE-SW less than
10 kt early Sunday, then SW-NW 5-15 kt Sunday night.

&&

.AIR STAGNATION...High pressure aloft will continue through
Sunday night, with daytime mixing heights peaking between 1500
and 2500 feet AGL in the valleys. Relatively light winds and a
low-level inversion will continue to limit ventilation in most
valleys. A cold front late Sunday into early Monday morning
will bring increased west to northwest winds, improving mixing
and ventilation.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Monday night...An upper level ridge
over the region today into Sunday will bring dry and stable
conditions. Fog and stratus have been limited by high clouds and
light southerly winds so far this morning. We could see an
increase in Fog/Stratus coverage for the Snake River Plain later
this morning between 7 AM and 10 AM, with the best chance
across south central Idaho, including the Magic Valley. Valleys
and basins in eastern Oregon and west central Idaho will also
see periods of fog through the early afternoon. However,
widespread dense fog advisory appears unlikely at this time. We
will end the Dense Fog Advisory for all zones except the Western
Magic Valley.

Drying south to east winds are expected to increase this
afternoon, which will help lift and dissipate fog and stratus,
yielding mostly sunny conditions for most. Stratus could remain
longer across the sheltered valleys of eastern Oregon. The
increased winds today along with mostly clear skies should allow
temperatures to warm about 4 to 7 degrees above normal.

High res models indicate stratus redeveloping tonight mainly
across the Lower Treasure Valley and Upper Weiser Basin along
with Baker Valley. This is pretty typical for this type of event
as what remains of the boundary layer moisture pools at the
lowest part of the valley. Given the drier near surface air,
widespread fog appears unlikely.

Warm and dry on Sunday with increasing southeasterly surface
winds ahead of the next cold frontal passage. This system will
move across the region late Sunday into early Monday, bringing
precipitation mainly to the Central Idaho mountains Monday
morning. There is about a 20 percent chance of rain showers in
the valley Monday morning. Snow levels start out around 6000
feet Sunday night and fall to between 2500 to 3500 feet late
Monday morning with passage of the front. Thus, light snow is
possible above 5000 feet, with between 1 to 2 inches expected.
Breezy northwesterly winds will bring near normal temperatures,
which should mix out the valley inversion.

LONG TERM...Tuesday through Saturday...The front end of a
large amplifying ridge is expected to build into the region
Tuesday through Thursday. This ridging will bring drier
conditions through most of Tuesday, but peak lower elevation
temperatures are expected to remain in the lower 40s. Valley
temperatures are expected to take on a slight warming trend from
the mid/upper 40s into the lower 50s Wednesday through Friday.
The aforementioned ridging pattern is expected to steer a plume
of moisture off the Pacific NW coast into the area late Tuesday
to the end of the week, favoring a 20-30% chance of
precipitation in lower elevations and a 50-60% chance in higher
elevations everyday of the extended forecast period. Snow levels
are expected to take on an upward trend from the 3000-4000 ft
range Tuesday and early Wednesday into the 5000-6000 ft range
late Wednesday to the end of the week. Mountain locations may
get some wintry mix in precipitation throughout the week. A
longwave trough, with some guidance uncertainty on the arrival
pattern, is generally expected to dig into the area Friday
through Saturday, favoring widespread precipitation and a
cooling trend throughout the area towards the end of the
extended.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Dense Fog Advisory until 10 AM MST this morning IDZ016.
OR...Dense Fog Advisory until 9 AM PST this morning ORZ062.

&&

$$

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DISCUSSION...MC
AVIATION.....NF
AIR STAGNATION...MC
SHORT TERM...JDS
LONG TERM....JY