128
FXUS65 KBOI 230354
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
854 PM MST Sat Nov 22 2025

.DISCUSSION...Aside from an area of low stratus across
southeast Oregon between Baker City and Ontario, skies are
mostly clear this evening. Radiational cooling and relatively
light winds will allow areas of fog and low stratus to redevelop
overnight into Sunday morning. Dense fog remains a possibility,
with the highest potential in the Boise metro area, portions of
the Magic Valley, and valleys across southeast Oregon where
the HREF depicts a 30-60% chance of visibilities 1/4 mile or
less. Will continue to monitor trends, but a Dense Fog Advisory
may be needed in future updates. Otherwise, conditions Sunday will
be very similar to today, with low stratus/fog lifting and
decreasing in the afternoon. The next significant change in the
weather will arrive Sunday night into Monday as a cold front
moves across the area.

&&

.AVIATION...MVFR to LIFR in areas of fog/low stratus developing
overnight into Monday morning. Best chance for LIFR will be in
valleys/basins of E-central OR, Lower Treasure Valley, and
portions of the Magic Valley, with lower chances elsewhere.
Improving by Sunday afternoon. Cold front with rain/snow
arriving from the NW Sun night. Surface winds: variable 10 kt or
less. Winds aloft at 10kft MSL: SW to W 10-20 kt.

KBOI...VFR this evening. Fog/mist expected to arrive in the
vicinity of KBOI from the W or NW around 23/05Z-06Z, which could
bring visibility down to MVFR. There is a 25% chance of
dropping to LIFR visibility by 23/12Z, increasing to 45% chance
of LIFR around sunrise. This uncertainty is due to southeast
winds battling the fog progression. Surface winds: SE 3-7 kt.

&&

.AIR STAGNATION...High pressure will keep stagnant air in place
on Sunday. Daytime mixing heights will be 1500 to 2500 feet AGL.
Relatively light winds and a low-level inversion will continue
to limit ventilation in most valleys. A cold front Sunday night
into Monday morning will remove the inversion, which will
combine with breezy west to northwest winds to improve mixing
and ventilation.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Monday night...Another round of
stable conditions are expected overnight into most of Sunday as
flat high pressure remains in control. There is strong agreement
that low stratus and fog will develop overnight. The latest
guidance indicates a 60-80% chance of stratus/fog for the Lower
Treasure Valley of Oregon and Idaho and the Magic Valley, with
a 30-50% chance for the Baker and Magic valleys. There is
potential for dense fog with visibilities less than 1/4 mile in
the Lower Treasure Valley and eastern Magic Valley (30-40%
chance) by early morning Sunday.

A Pacific storm system is expected overnight Sunday into Monday,
with the majority of precipitation anticipated north of the
Snake River Valley in the central mountains. Winds will pick up
behind the system during the day on Monday as well. Snow levels
will generally be above 5000 feet with 1 to 3 inches possible.

LONG TERM...Tuesday through Saturday...Unsettled conditions
prevail through the long term. Tuesday is looking to start out
dry but with increasing high clouds as mid-level moisture makes
its way around the ridge to our west. By late Tuesday/early
Wednesday, the bulk of the moisture advection will be overhead
allowing for increasing chances of precipitation chances of
20-70% across much of the area, generally increasing as you move
from south to north. Snow levels start out at 2-3 kft MSL
Tuesday night, so the Snake Plain could see a wintery mix early
Wednesday morning before snow levels rise to 4-6kft MSL. Through
the latter half of the week, there is good model consensus of
the ridge moving over our area. The area will begin to dry out
Thursday; however, A shortwave grazing our northern zones late
Thursday/early Friday will keep elevated precipitation chances
(20-50%) in Baker county, the west Central Mountains, and Boise
mountains. That shortwave, and the system evolution following
it, is helping mitigate air stagnation concerns despite general
ridging over our area.

Friday into the weekend, Confidence is increasing in a trough
digging down over our area. This trough is leading to elevated
precipitation chances (50-70%) across the majority of our area
Friday evening through Saturday. Uncertainty does, however,
remain regarding just how deep the trough will get. This is
resulting in some uncertainty with how much we will cool off
over the weekend, and how just low the snow level drops.
Temperatures begin near normal on Tuesday, increasing to 5-10
degrees above normal Thursday. Temperatures will begin to cool
off through the weekend, but as noted earlier, uncertainty
remains to what degree; for now, am maintaining temps near
normal for Saturday.

&&

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

&&

$$

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DISCUSSION...ST
AVIATION.....SH
AIR STAGNATION...ST
SHORT TERM...MC
LONG TERM....NF