590
FXUS65 KBOI 040417
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
917 PM MST Wed Dec 3 2025

.DISCUSSION...A few high clouds are moving across the area this
evening ahead of the next Pacific system. These clouds are not
expected to impact overnight temperatures, which will once again
drop into the mid-20s across the Snake River Plain. The next
moist system remains on track to reach the area Thursday
afternoon, bringing widespread precipitation that will continue
into early Saturday. A critical feature of this event is the
warm frontal passage, which will see the snow level climb to
5,550 feet early Friday morning; all areas below this elevation
will transition to rain. Mountain valleys, including the Long
Valley of Idaho, are expected to see snow continue until early
Friday afternoon before mixing with rain. Most latest guidance
has lowered the Quantitative Precipitation Forecast (QPF) for
this event, with a blend of models suggesting an overall 15-25%
reduction from this morning. This adjustment has resulted in a
minor lowering of mountain snow amounts by about an inch from
the previous forecast, though travelers along Highway 55 and
Highway 21 in southwest Idaho should still be prepared for
winter conditions.

For the Snake River Plain, surface temperatures are generally
forecast to be near the mid-to-upper 30s Thursday night and
remain steady. The HREF model shows the highest snow chance (40%
between 3 PM and 7 PM Thursday), but even this guidance favors a
60% chance of rain during that window, and most other high-
resolution guidance still strongly favors rain over snow. Even
if precipitation were to start as snow or a mix, it is very
unlikely to accumulate before the warm front moves across the
valley around midnight, causing precipitation to quickly
transition to all rain. Either way, wet roads are expected for
the Friday morning commute.

&&

.AVIATION... Areas of IFR/LIFR fog/low stratus tonight into early
Thursday morning, mainly near KBNO, mountain valleys, and north of
the Western Magic Valley. Otherwise, mainly VFR conditions overnight
and early Thursday morning. Lowering BKN/OVC ceilings through
Thursday late morning/early afternoon. Widespread rain/snow over
most areas Thursday afternoon/evening, with IFR/LIFR ceilings/fog
and mountain obscuration. Surface winds: light and variable under 6
kt overnight. Winds aloft at 10kft MSL: N/NW 10-20 kt.

KBOI...VFR. A 15% chance of MVFR/IFR fog/low stratus Thursday
morning, with a higher chance along the foothills. Mainly VFR
Thursday morning/early afternoon, then rain with possible snow mix
(around 20%) with VFR/MVFR ceilings in the afternoon/early evening.
Surface winds: mostly light and variable under 6 kt tonight,
becoming SE 3-6 kt overnight through Thursday morning.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Friday night...The atmosphere is
expected to direct a system up and over the ridge of high
pressure to our west beginning mid day Thursday through the
remainder of the short term period. Current satellite depicts a
broad swath of moisture ahead of this Pacific system, and model
data is in good agreement that widespread precipitation is
expected. Guidance hints that precipitation will arrive in
eastern Oregon by mid day Thursday then into southwest Idaho by
mid/late afternoon. Snow levels will initially be near valley
floors early in the day, rising to above 5500 feet overnight
into early Friday. There exists uncertainty with how long the
low level cold pool will remain in place across the Treasure
Valley and Weiser Basin. This could push back the changeover
from snow to rain in these areas. Guidance suggests a 10% chance
of 0.1 inches of snow for the Lower Treasure Valley and a 30%
chance of at least 0.5 inches of snow for the Weiser Basin.
Current guidance does not include accumulating snow in other
lower valley locations, such as the Upper Treasure Valley of
Idaho, but the chance of snow falling is above 60%. By early
Friday morning all areas below 5500 feet will have transitioned
to rain. For the mountain valleys, including the Long Valley of
Idaho, guidance suggests a 30% chance of greater than 4 inches
of snow late Thursday through the afternoon Friday. Travelers
along Highway 55 and Highway 21 in southwest Idaho should be
prepared for winter conditions. We will be monitoring for the
need to issue a winter weather related advisory for portions of
the central mountains of Idaho.


LONG TERM...Saturday through Wednesday...Unsettled conditions
will continue through the weekend and into early next week as
moisture continues to stream over the top of the Pacific ridge
of high pressure. There is strong agreement amongst ensemble
model data that two periods of mountain snowfall are possible,
one Saturday through Sunday Night, and the second Tuesday into
mid week. Snow levels are expected to linger between 4500 and
6000 feet this weekend, before rising to around 7000 feet by
Tuesday. Travelers and recreators should anticipate winter-like
conditions in the mountains and along mountain roadways during
this period.


&&

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

&&

$$

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DISCUSSION...JDS
AVIATION.....JY
SHORT TERM...MC
LONG TERM....MC