750
FXUS65 KBOI 090954
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
254 AM MST Tue Dec 9 2025

.SHORT TERM...Today through Thursday night...Warm, moist
air mass, with an atmospheric river extending across the
eastern Pacific along 45N then E-SE-ward through our CWA,
will continue through Wednesday. The atmospheric river
will produce moderate to locally heavy rain in the northern
third of our CWA, i.e., Baker County/OR, and Idaho north of
the Snake Basin, with snow level staying above 8000 feet MSL.
Northern rivers will run higher but should stay safely below
flood stage, with most cresting Friday. The atmospheric river
and steady rain will shift slowly north Wednesday and Thursday
allowing our CWA to dry out. High temps today will be several
degrees warmer than yesterday as yet another warm front passes
through, and Wednesday looks warmer still, reaching 60 degrees
in many southern valleys. Only slight (1-3 degree) cooling
Thursday. On the other hand, partial clearing will allow
colder nighttime lows and patchy fog in wind-sheltered
southern valleys. Winds through Thursday will be light to
moderate southeast through southwest, strongest in south-
central Idaho this afternoon with gusts 30 to 35 mph.

.LONG TERM...Friday through Tuesday...Come Friday, a building
ridge will have pushed the jet stream and Pacific moisture
plume north of our area. With high pressure setting in beneath
the ridge, we will be looking at dry conditions with partly
cloudy skies through Sunday. While the ridge will keep our
area dry, it will introduce its own subset of hazards. Model
soundings show valley inversions developing under the
subsidence aloft, This is also marked by mixing heights below
2000 ft AGL. With the added surface moisture, thanks to the AR
event in the short-term, fog and low stratus will likely be in
play Friday- Sunday. Another consequence of the inverted
conditions is increased uncertainty with regard to temperatures.
While a warmer airmass will be in place, colder air could get
trapped in the valleys. For now, am maintaining temperatures
10-15 degrees above normal (at the higher end of that range on
Friday, gradually decreasing toward the lower end by Sunday).
The added caveat would be in the inversion influence, by both
the cooler air trapping and fog/low stratus. This could tamper
down temps below the inversion... and un-luckily for us, are
not captured well by the guidance, especially this far out.

Beyond Sunday, unsettled conditions will make their way back
into the forecast. A shortwave and its associated cold front
is set to flatten down the ridge early this coming week.
However, the timing of the first system is still tricky to pin
down. While the GFS and Euro ensemble suites agree on a system
early next week, they diverge on the timing. The Euro suite
brings the system in earlier Monday, whereas the GFS suite is
lagging a little behind and holding off until late Monday/early
Tuesday. In either case, this supports increasing precipitation
chances come Monday, increasing further through Tuesday.

&&

.AVIATION...Precip continuing across far E-Oregon and much of
SW-Idaho. VFR conditions in light precip and MVFR/LIFR ceilings
in heavier rain and high-elevation snow. LLWS through the
morning. Snow Levels: 6.5-7.5 kft MSL north of the Snake Plain,
8-9.5 kft MSL in/south of the Snake Plain. Surface winds: SW-SE
5-15 kt SW with gusts to 20-35 kt outside of the Treasure
Valley. Winds aloft at 10kft MSL: W-NW 40-55 kt.

KBOI...Generally VFR with light rain continuing through this
evening, periods of MVFR ceilings this afternoon. Threat of
LLWS through the morning. Surface winds: SE 8-12 kt this
morning, becoming northerly up to 10 kt this afternoon.

&&

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

&&

$$

www.weather.gov/Boise

Interact with us via social media:
www.facebook.com/NWSBoise
www.x.com/NWSBoise

SHORT TERM...LC
LONG TERM....NF
AVIATION.....NF