355
FXUS65 KBOI 180326
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
826 PM MST Mon Nov 17 2025

.DISCUSSION...Quiet wx in our CWA as an upper trough splits as
it moves inland from the coast tonight. The south portion of
the trough has become a closed low near San Francisco, headed
toward southern California Tuesday like the previous upper low,
while the north portion is forecast to move rapidly eastward
along the Canadian border, leaving our CWA under weak flow
aloft. The only pcpn should be light rain (light snow above
7000 feet Tuesday and 6000 feet Wednesday) in the West Central
ID mountains as the north part of the trough moves past. More
impactful wx might be valley fog Tuesday morning, patchy but
possibly dense. Would be more concerned with a ridge overhead
and an inversion below, or if the ground were snow-covered,
but neither is expected. In any case, patchy fog will be there
Tuesday, and to a lesser extent Wednesday, during morning
commute time. Current forecast looks good vs latest models
through Wednesday night so no updates should be needed.

&&

.AVIATION...Pockets of MVFR/IFR from low clouds will persist
across southeast OR and the southwest ID mountains overnight
through Tuesday morning. Widespread mountain obscurations.
Patches of LIFR fog will develop tonight into Tuesday morning,
possibly continuing through afternoon. Surface winds: variable
under 10 kt. Winds aloft at 10kft MSL: S-SW 5-15kt.

KBOI...Mainly VFR through the evening and overnight with ceilings
above 5000 ft AGL. A 20-30% chance of LIFR low clouds/fog
developing Tuesday AM, highest west of KBOI. Surface winds
SE or variable 5 kt or less.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Wednesday night...A weak ridge
will build back into the region this evening, bringing drying
conditions and helping the showers across the area to taper off.
Two cutoff lows will skirt our region today and tomorrow, with
one diving down to the south and another moving north. This
situates us in the deformation zone between the lows, with
mostly dry conditions. Warm and moist southwest flow will
continue to bring intermittent cloud cover tomorrow over the
region, with clearing overnight allowing for fog formation in
area valleys on Tuesday and Wednesday morning. There`s medium
confidence in dense fog formation resulting in visibilities
below 1/4 mile in lower elevation valleys tomorrow. A weak cold
front will move into the region on Wednesday, bringing a 20-40%
chance of mountain snow above 5000-6000 feet with valley rain in
Baker County and the West Central Mountains. Temperatures will
continue to cool throughout the short term period, but still be
about 5-10 degrees above normal, with daytime highs in the Boise
area in the mid to upper 50s through Wednesday.

LONG TERM...Thursday through Monday...A very similar pattern to
recent days will continue in the extended. An upper level trough
will split at it approaches the coast on Thursday. The southern
portion will develop into a cutoff low and move south into
California, resulting in only a 20-40% chance of showers across our
area. High pressure will then build overhead through the weekend. A
temperature inversion may develop under stable conditions, and low
clouds/fog may become persistent in the lower elevations if enough
moisture gets trapped under the inversion. Temperatures are expected
to average slightly above normal across the area, but if low clouds
and fog do develop, that would reduce high temperatures.

Moisture is expected to move over top of the ridge late in the
weekend into early next week. Ensembles favor the ridge to be strong
enough to keep the moisture to our north through Sunday, resulting
in lower precipitation chances than previous forecasts over the
weekend. On Monday, an upper level trough approaching the coast will
bring a 30-60% chance of precipitation, with the highest chances in
the northern mountains. Snow levels around 4500-6000 feet will keep
precipitation as rain in the lower elevations, with snow
accumulations limited to the mountains.

&&

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

&&

$$

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DISCUSSION...LC
AVIATION.....JY
SHORT TERM...SA
LONG TERM....ST