144
FXUS65 KBOI 231646
AFDBOI

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

.DISCUSSION...Morning satellite imagery and observations
indicate a broad area of low stratus and fog across the lower
Treasure Valley of Oregon and Idaho. This area has been eroding
slowly from east to west, and this trend is expected to continue
throughout the day today. Areas of dense fog are present as
well, especially from Caldwell westward to Ontario. This fog
will become patchy by late morning, before dissipating by early
afternoon. Will allow the Dense Fog Advisory to drop at 10am
MT/9am PT. No updates to the current forecast planned this
morning.

&&

.AVIATION...Areas of LIFR to MVFR in fog and low stratus. Conditions
improving to VFR area-wide through late morning/early afternoon.
Precipitation beginning after Mon/00z, moving W-E along a cold
front. MVFR/IFR conditions possible in snow/wintery mix and low
clouds. Mtns obscured in precip. Snow levels: 5-6 kft MSL, Lowering
to 2.5-4.5 kft MSL Monday afternoon. Surface winds: Variable up to
10 kt. Winds aloft at 10kft MSL: W 5-15 kt.

KBOI...VFR. Rain showers early Monday morning, most likely time for
rain at terminal is between Mon/12z-Mon/16z. Surface winds: light
and variable this morning and afternoon.

&&

.AIR STAGNATION...Another round of stagnant air today with an
inversion well established across the region. A cold front will
likely disperse the inversion overnight with improved mixing
Monday into Tuesday.

&&

.PREV DISCUSSION...
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.

&&

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