919
FXUS65 KBOI 231004
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
304 AM MST Sun Nov 23 2025

.SHORT TERM...Today through Tuesday night...Dense fog has
formed across much of the Lower Treasure Valley this morning
and is slowly expanding eastward into the Upper Treasure Valley,
affecting areas including Meridian, Eagle, and Boise. This
development has been captured consistently well in the latest
high resolution model runs, with East Boise being the farthest
eastern extent of the fog progression. Caution is advised when
traveling from Ontario to Boise this morning, as the fog may not
be continuous. We have issued a Dense Fog Advisory through 11
AM today, with the Ontario, Fruitland, and New Plymouth areas
expected to be the last to escape the low stratus.

Stratus erosion in the valley will be aided by increasing
southeasterly surface winds this afternoon ahead of the next
upper level trough and cold front. This will help keep
temperatures well above normal for this time of year, with
readings expected to be 4 to 8 degrees above average. This
incoming system will move across the region early Monday. The
best chance for precipitation (50 percent probability) is mainly
over the Central Idaho mountains Monday morning, while there is
a lower probability, about a 20 percent chance, of rain showers
in the Treasure Valley. Snow levels will start around 6000 feet
Sunday night and are then expected to fall significantly to
between 2500 and 3500 feet late Monday morning with the front`s
passage. Light accumulating snow is expected above 5000 feet,
with up to 2 inches possible. Breezy northwesterly winds
following the front will bring near normal temperatures, which
should completely mix out the valley inversion.

What has been a consistent pattern this November, an upper level
ridge of high pressure will once again build over the Pacific
Northwest starting Tuesday. This development is highly probable
and will place a cold northwesterly flow over the area, keeping
temperatures around seasonal norms.

.LONG TERM...Wednesday through Sunday...A large ridge is
expected to continue building over the area Wednesday through
Thursday. A slight warming trend will bring daytime temperatures
in lower elevations from the mid-to-upper 40s Wednesday to the
lower 50s Thursday, while higher elevations will continue seeing
peak temperatures in the mid 30s to lower 40s on both days.
This ridging pattern is still expected to steer moisture off the
Pacific NW coast into the area, bringing a 20-30% chance of
precipitation for lower elevations and a 50-70% chance for
higher elevations on Wednesday. A weak shortwave trough will dig
North of the area late Thursday into early Friday, bringing a
30-40% chance of precipitation for higher terrain areas on
Thursday. The slight warming trend is expected to increase snow
levels back up into the 5000-7000 ft range from Wednesday to
Friday, so the central mountains of SW ID and SE OR may see
wintry mix in precipitation throughout the week. A large-scale
trough digging across W`rn Canada and the NW region is expected
to return a cooling trend and precipitation over the entire area
Friday through Sunday, though considerable uncertainty over the
longwave trough`s arrival remains.

&&

.AVIATION...MVFR to LIFR in areas of freezing fog/low stratus
developing overnight into Monday morning. Highest chances for LIFR
fog/stratus in valleys/basins of E-central OR, Upper Treasure
Valley, and portions of the Magic Valley, with lower chances
elsewhere. Conditions improving by Sunday afternoon. Cold front with
rain/snow arriving from the NW Sunday night/early Monday morning.
Surface winds: variable or SE 10 kt or less, becoming SW-NW under 7
kt Sunday afternoon. Winds aloft at 10kft MSL: SW to W 10-20 kt.

KBOI...Freezing fog/mist from NW overnight through late morning
around 16Z, with intermittent periods of clearing possible. 10-20%
chance of precipitation Sunday night/Monday early morning. Surface
winds: SE 3-7 kt early morning, becoming NW 3-7 kt late
morning/early afternoon.

&&

.AIR STAGNATION...High pressure will keep stagnant air in place
today. 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 tonight into
Monday morning will remove the inversion, which will combine
with breezy west to northwest winds to improve mixing and
ventilation.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Dense Fog Advisory until 10 AM MST this morning IDZ012-014-033.
OR...Dense Fog Advisory until 10 AM MST /9 AM PST/ this morning
     ORZ064.

&&

$$

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SHORT TERM...JDS
LONG TERM....JY
AVIATION.....JY
AIR STAGNATION...JDS