835
FXUS65 KBOI 062131
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
231 PM MST Sat Dec 6 2025

.SHORT TERM...Tonight through Monday night...Unseasonably warm
conditions continue through the entire forecast period.
Temperatures are already above guidance. A record high has been
set today at Ontario OR with 56 degrees as of 2pm MST. Westerly
flow continues to bring scattered snow showers over the
mountains through this evening with minimal accumulations. A
weak warm front moves over the area on Sunday, keeping
temperatures slightly cooler than today, with precipitation
during the daytime heating hours. Then temperatures continue to
warm on Monday with another warm frontal passage late. Rain
arrives Monday afternoon, generally north of a line from Burns
OR to Twin Falls ID. Temperatures on Monday reach the low to mid
50s across the Snake Basin and eastern OR lower elevations with
unusual vertical mixing persisting.

.LONG TERM...Tuesday through Saturday...The long term remains
mostly wet and active as atmospheric river continues to supply
warm tropical moisture over a strong eastern Pacific ridge. The
flow in the moisture plume reaches a staggering 50-80 knots at
500mb in the middle of next week, with PWs near record levels
for this time of year moisture flux will be significant.
Precipitation chances every 6 hours Tuesday through Thursday
morning are around 80-100% north of a line from Ontario, to
Boise, to Fairfield centered primarily in the high terrain of
eastern Oregon and west central Idaho. South of that line,
precipitation chances are still elevated at 40-60%. The very
strong advection of warmer air brings snow levels to the moon,
7-9 kft MSL. This is still low enough for the very highest peaks
to see snow, but many low mountain ranges and mountain valleys
are likely to see predominately rain through the event. Summits
that see snow could see 1-2 feet of snow, but below 8000 ft any
snow that falls will be wet and followed by periods of rain.
North of the Ontario, Boise, Fairfield line in the high terrain;
rainfall/liquid equivalent totals at 1-2.5 inches. South of the
line closer to 0.2- 0.5 inches, with some portions of far SE
Oregon only seeing a few hundredths of an inch. The strong winds
aloft will mix down to the surface, bringing gusts of 25-45 mph
to open areas, ridges, and highlands. The Tuesday to Thursday
morning period weather will be most significant on Wednesday as
a shortwave supplements the pattern, bringing the strongest
winds and highest rainfall rates.

Late Thursday through Saturday the high pressure begins moving
inland, pushing the moisture stream north and bringing drier
weather. With the ridge overhead, valley inversions, low
stratus, and fog are all possible. The warmer airmass in the
atmospheric river and high pressure following will raise surface
temps to nearly 20 degrees above normal throughout the long
term. Possible inversions late in the week could trap colder air
near the surface, raising uncertainty in temperature forecasts
after Thursday.

&&

.AVIATION...Rain/snow showers and MVFR-IFR ceilings continue in
the W-centrl mtns and E OR. A brief drier period is expected
tonight with patchy valley fog or stratus before widespread
precipitation begins to move into the area Sunday afternoon.
Snow levels: 4.5-5.5 kft MSL. Surface winds: W-NW 10-20 kt, with
gusts to 20-30 kt in open areas and ridges becoming light and
variable tonight. Winds aloft at 10 kft MSL: W-NW 20-35 kt.

KBOI...VFR. A slight chance of showers in the vicinity this
evening. Surface winds: NW 8-12kt with gusts to 20 kt becoming
SE less than 6 kt this evening.

Sunday Outlook...Widespread precipitation through
afternoon/evening. Snow levels: 4-6 kft MSL in the morning,
increasing to 5-7 kft MSL in the afternoon. Surface winds: SE-SW
5-15 kt.

&&

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

&&

$$

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SHORT TERM...KA
LONG TERM....JM
AVIATION.....JM