473
FXUS65 KBOI 080350
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
850 PM MST Sun Dec 7 2025

.DISCUSSION...Radar pcpn echoes have generally ended in our CWA
this evening and no further pcpn is expected overnight and most
of Monday. A well-defined atmospheric river along 40-45N in the
Pacific was nearing the WA coast this evening, and models aim
it across the northern zones of our CWA Monday evening. This
will begin a lengthy period of moderate to heavy rain (snow
level 7000-8000 feet) in our northern zones Monday night
through Wednesday, with the atmospheric river shifting slowly
northward as a warm front. Wednesday will become unseasonably
warm (and drying by Thursday) and will stay warm and dry
through Saturday. Saturday may be so warm aloft that an
inversion will form in the valleys below, but with little if
any snow on the ground the inversion should be weak. A cooler
upper trough is finally forecast inland from the north Pacific
next Sunday. No sign of winter weather through at least Dec 14.
No updates.

&&

.AVIATION...Generally VFR, except low stratus/fog in mountains
creating mtn obscuration. Patchy valley fog Monday AM. Precip
increasing from the northwest Monday PM, heaviest north of Snake
Plain. Periods of MVFR-LIFR in moderate/heavy rain, or in snow.
Snow levels Monday PM: 7k-8k feet MSL in E Oregon, 6k-7k feet
in SW Idaho. Surface winds: SW-SE 5-15 kt, Monday PM gusts to
20-30 kt in E Oregon and mtns of SW Idaho. Pockets of LLWS
tonight, including KEUL-KBOI. Winds aloft at 10kft MSL:
NW 25-40 kt.

KBOI...Generally VFR, but up to 10% chance of low ceilings/mist
developing early Monday AM. Low level wind shear tonight,
decreasing after Mon/09Z. Rain returns after Tue/00Z. Surface
winds: SE 4-10 kt.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Tuesday night...A weak warm front
has brought light precipitation to the area today. Precipitation
should taper off later this afternoon with mild temperatures
continuing. A lull in precipitation is expected on Monday before
another warm front moves through. The next warm front arrives
on Monday evening, with widespread precipitation north of a
line from Burns OR to Jerome ID through Tuesday night. Warm and
moist zonal flow continues over the next several days as a
significant atmospheric river impacts the Pacific NW across WA,
northern ID and western MT. The central ID mountains will see
significant precipitation, but far less amounts compared to
northern ID. Snow will be confined to the highest peaks above
7000-8000 feet.

LONG TERM...Wednesday through Sunday...Low pressure aloft in
the Gulf of Alaska and high pressure off the coast of
California are creating a strong pressure gradient, pulling a
significantly warm and moist airmass through the area Wednesday
through Thursday. Mid-level flow remains at 50-70 kt with PWs
near records for this time of year. Winds in ridges, open areas,
and highlands gust up to 45 mph at the surface. These winds,
orography, and the moisture will bring an extended period of
precipitation chances greater than 70% in higher terrain.
Rainfall/liquid equivalent Wednesday through Thursday is an
extra 0.5-1.5 inches in higher terrain and up to 0.1 inches
in lower elevations on top of what fell in the short term.
The strong flow and warm airmass bring snow levels up to a
staggering 7-9 kft MSL both of these days, so while the
highest peaks will see half a foot to a foot of snow,
mountains below about 8kft MSL will see predominantly rain.
The prolonged rainfall on a barely developed snowpack would
produce runoff and have long-lived impacts on the snowpack
going into the winter.

The strong flow aloft tapers off into Friday as the moisture
plume goes north of the Pacific high as it moves inland. The
weather will generally dry out and winds will die down as the
ridge builds overhead. The ridging will make valley inversions
possible and thus fog and low stratus with saturated soils. With
the warmer airmass, temperatures above any inversion will be
15-20 degrees above normal throughout the long-term period.
The possibility of inverted conditions introduces uncertainty
in valley temperatures late in the week as colder air could
get trapped near the surface. Models begin to diverge by the
end of Sunday, with some hints at a return to colder temps
and more precip in the extended forecast.

&&

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

&&

$$

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DISCUSSION...LC
AVIATION.....SH
SHORT TERM...KA
LONG TERM....JM/LC