051
FXUS65 KBOI 200356
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
856 PM MST Wed Nov 19 2025

.DISCUSSION...Much of the stratus coverage has become disrupted
in far southwest Idaho due to isolated showers and mid level
clouds this evening ahead of the next low pressure system.
Meanwhile, the well-established low cloud deck in E Oregon and
west-central Idaho continues on, with some expansion expected
tonight before the next wave of precipitation moves in. Latest
hi-res models depict scattered showers first developing in east
Oregon overnight, then into southwest Idaho by early/mid
morning. As the upper low approaches from the west, a broader
swath of precip will arrive with an occluded surface front
around mid morning. Momentum of this precip band will slow and
stall in east OR and far southwest ID once the upper low dives
south into California and Nevada. Precip will begin to taper off
in the afternoon and become isolated through the evening. Snow
levels are currently 6500-7500 feet MSL, but are forecast to
lower from west to east to 5500-6500 feet by Thursday afternoon.
Areas of fog and stratus should make a return Thursday night,
except will be limited in east-central Oregon where an increase
in northwest surface winds are expected.

&&

.AVIATION...Areas of MVFR/IFR in low stratus in E Oregon and
W-central Idaho, and in isolated showers in SW Idaho. Precip
coverage expanding from the west overnight and Thursday morning.
Continued degraded conditions expected, with MVFR/IFR and local
LIFR in precip and low ceilings. Mtns obscured. Snow levels
5500-7500ft MSL. Surface winds: variable less than 10 kt. Winds
aloft at 10kft MSL: S to SW 10-20 kt.

KBOI...Periodic MVFR with light rain showers and stratus
tonight. MVFR ceilings expected to become predominant beginning
around 20/12z, as shower coverage increases across southwest
Idaho. Rain will taper off Thursday afternoon, with the return
of stratus or fog likely Thursday night. Surface winds light and
variable.

&&

.AIR STAGNATION...High pressure will develop and strengthen
beginning Friday, with stable conditions persisting through
early Monday. Conditions will be borderline for air stagnation,
with the uncertainty due to mixing heights hovering around or
slightly above 2000 feet AGL. However, relatively light winds
with a dry, inverted boundary layer will support poorer
ventilation in valleys.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Friday night...Valley stratus and
patchy fog were slowly decreasing this afternoon and should be
less extensive tonight than last night. North Pacific cold front
will move onshore late today, then weaken as it moves further
inland, finally dissipating in eastern OR early Thursday morning.
The supporting upper trough will split with the southern end
becoming a closed low in California Thursday, while the north
portion continues eastward along the Canadian border. Light
rain with the front will get only as far east as Malheur County
before the front dissipates. However, hi-res models show another
area of light rain (.05 inch at most) in western Idaho Thursday.
Drying is expected in our CWA Thursday night through Friday
night with the closed low moving to southern California and the
northern trough well east of our area. As the low and trough
move away from each other an upper ridge will develop over our
area Friday. The ridge will gradually cause an inversion in the
valleys below with more fog and low clouds. High temps Thursday
and Friday will continue around 5 degrees above normal. Lows
will cool several degrees each night, back to normal Friday
night. No significant winds.

LONG TERM...Saturday through Wednesday...A high pressure ridge
with weak NW flow will keep temperatures moderated at 5-10
degrees above normal this weekend. Dry weather with partly
cloudy skies and light winds is expected during this time.
However, the only wrench in the forecast are some low mixing
heights (1800-2500 ft AGL) which are borderline favorable for
an inversion developing. Stratus under an inversion would
result in daily highs colder than forecast, but right now
the inversion only has a 20% chance of building. Monday,
temps remain warmer than normal but the region will be clipped
by the southern end of a broad trough as it moves across the
US/Canadian border. This will bring a 20-30% chance of
precipitation in high terrain, snow above 5-6 kft MSL, and
the stronger NW flow behind the trough will bring colder air
on Tuesday and Wednesday, with temps finally dropping to near
normal for this time of year.

&&

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

&&

$$

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DISCUSSION...SH
AVIATION.....SH
AIR STAGNATION...SH
SHORT TERM...LC
LONG TERM....JM