499
FXUS65 KBOI 190348
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
848 PM MST Tue Nov 18 2025

.DISCUSSION...A slow-moving trough is steering a band of mid-
to-high clouds over E-Central OR and into the area, with patchy
fog and areas of stratus ahead of it, and expected to continue
over SW ID and SE OR through Wednesday morning and early
afternoon. Winds will remain on the variable and calmer side
tonight, becoming more E-SE Wednesday afternoon and dissipating
much of the fog. Patchy valley fog and areas of stratus are
expected to return Wednesday night through Thursday morning, as
a secondary trough off the Pacific NW coast digs across the
area. A 20-40% chance of precipitation is still expected mainly
for the W-Central ID mountains Wednesday. Thursday will see a
20-30% chance of precipitation mainly across higher elevations.
Peak daytime valley temperatures are expected to remain in the
lower 50s Wednesday through Friday, with nighttime temperatures
slowly dropping into the mid/lower 30s. Higher elevations will
generally see daytime temperatures in the upper 40s and
nighttime temperatures in the upper 20s and lower 30s Wednesday
through Friday.

&&

.AVIATION...MVFR-LIFR in areas of fog/low stratus, especially in E
Oregon and Wrn Snake Plain. Light precip for NE Oregon and W-central
Idaho Wed morning, with 6.5k-7.5k feet MSL snow levels. Some Flight
Cat improvement expected by mid-day Wed, except lingering low
ceilings over SW Idaho mountains and E Oregon. Surface winds:
variable less than 8kt. Winds aloft at 10kft MSL: S to SW 5-15 kt.

KBOI...Periods of MVFR/IFR from low stratus expanding tonight in
the Treasure Valley. A 70% chance of LIFR ceilings/vis occurring
between 19/06z-15z. Uncertainty of LIFR is due to passing upper
low and presence of mid clouds. Surface winds: light and variable.

&&

.AIR STAGNATION...Forecasts keep conditions borderline in
regards to a prolonged stagnant air mass setting up. Mixing
heights of 1800-2500 feet AGL and light winds are expected
through Friday. The weekend will see a low-amplitude ridge which
will keep dry and stable conditions in place. Expect fog and
stratus to be in play through at least Wednesday with a system
on Thursday possibly breaking it up, especially in the Snake
Plain which gets into easterly winds.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Thursday night...We remain under
an area of weak flow aloft sandwiched between a low over
southern CA and another along the US/Canada border. This
northern system will hold the most potential impact for our
weather over the next 24hr as it drags a weak front across the
area. The front will bring a 20-40% chance of showers to the
e-central Oregon and w-central Idaho mtns on Wednesday and
enough wind to portions of SE Oregon to combat the development
of fog/stratus. Further east and south, the front is expected to
have little impact near the surface which will favor
redevelopment of fog and stratus tonight into Wednesday. Given
the stubbornness the fog/stratus has shown today, have leaned
into the HRRR and NAMnest solutions for tonight into Wednesday
regarding timing and coverage of low cloud cover. Expect to see
a mix of fog/stratus from Harney/Malheur counties through the
Snake Plain to Twin/Jerome. Not confident enough on the form and
coverage to issue any highlights for dense fog, but wouldn`t be
surprised if one is needed for Wednesday morning. Above the
valleys mid-high clouds will accompany the weak front and mtn
showers.

Another wave will push onto the coast late Wednesday, extending
into our region on Thursday. Not confident on what fog/stratus
will do Wednesday night but the lowest elevations stand the best
chance at seeing it return (if it does in fact erode on
Wednesday). This next system will bring a more widespread 20-30%
chance of precipitation to SE Oregon and the SW Idaho Thursday,
though any amounts will be light (most locations <0.10"). Snow
levels through the period will remain between 6-8kft so what
little does fall will be limited to the higher peaks.

LONG TERM...Friday through Tuesday...A ridge builds in from the
west as a closed low moves over southern California, this will
allow for a mostly zonal flow to keep temps moderated through
Monday at about 5-10 degrees above normal. During this period,
mixing heights have a daily maximum of around 2-3 kft MSL,
lowest on Friday and Saturday. This could allow a weak inversion
to develop, while supporting morning fog. A broad trough moves
in from Alaska Monday evening, bringing a 20-40% chance of
precipitation to the north and cooling temperatures down to
normal on Tuesday. Models seem less confident in the
precipitation than previous runs, but the trough is consistent
so a cooldown is likely.

&&

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

&&

$$

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DISCUSSION...JY
AVIATION.....SH
AIR STAGNATION...DG
SHORT TERM...DG
LONG TERM....JM