673
FXUS65 KBOI 170334
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
834 PM MST Tue Dec 16 2025

.DISCUSSION...No updates to the forecast this evening as Pacific
moisture streams inland from an atmospheric river. As the flow
aloft shifts southward over our CWA tonight it will push a
strong cold front through Wednesday morning. Ahead and along the
front precipitation chances are very high around 80-100% every 6
hours across the area. The precip will come in two waves, first
a stratiform broad shield this evening and then more showery
Wednesday morning along the cold front. Convective enhancement
in the showers could lead to locally moderate/heavy
precipitation. With snow levels still fairly high (7-9 kft MSL)
ahead of the colder airmass, most precip will fall as rain.
Lower elevations could see up to 0.25" of rain, higher
elevations will see a lot more due to orography, around 0.5-1".
High elevation passes and summits will see 4-7 inches of snow.

Along with the large storm total QPFs, winds become very strong
as flow aloft mixes down to the surface along and behind the
cold front. The low curvature of the driving trough and extreme
pressure gradient support gusts of 30-50 mph across the area,
potentially as high as 60 mph in S-Central ID and higher east of
our forecast area. Even sheltered valleys will see gusts up to
35 mph, so the Wind Advisory and High Wind Warning have been
allowed to continue.

The next round of precipitation comes Thursday, with a warm
front in the afternoon and subsequent cold front Friday night.
Ahead of the warm front Thursday, some lower elevations have a
brief shot at flurries or mixed precipitation, although as
precip onset has been shifting later in the day Thursday in
recent model runs, the surface may become too warm for valleys
to see snow. Mountains, however, could see a couple inches every
6 hours. While snow levels rise to 6-7 kft MSL behind the
warm front high elevation passes and summits will see 3-5
inches every six hours for a total of 8-15 inches through
Saturday morning. This has resulted in the issuance of a Winter
Storm Watch to account for possible travel impacts to high
mountain towns and in passes. The active weather is looking to
continue into the long term, see previous discussions for more
details.

&&

.AVIATION...Lowering ceilings as rain spreads across the area from
the SW this evening. Snow for elevations above 7-9 kft MSL. Low
VFR/MVFR in heavier rain, IFR/LIFR in snow. LLWS threat becoming
area-wide late tonight. Strong cold front will move through
Wednesday morning 12-18Z, ending pcpn but bringing strong, gusty
winds. Surface winds: SW-SE 5-15 kt with gusts to 20-30 kt,
increasing overnight to SW-S 15-30 kt with gusts 30-50 kt, locally
higher on mtn tops. Winds shifting to W-NW behind the cold front.
Winds aloft at 10kft: W-SW 25-40 kt, increasing to 45-70 kt
overnight.

KBOI...Mainly VFR. Rain developing this evening and continuing
overnight, with periods of MVFR possible in steadier rain. Low-level
wind shear threat increasing late tonight into Wednesday morning
ahead of the cold front. Surface winds: SE 5-10 kt, increasing to 10-
20 kt overnight with gusts up to 30 kt. Then W-NW 15-25 kt with a
brief period of 35-45 kt gusts beginning approx Wed/15Z with cold
front.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Thursday night...Lots of impactful
weather the next several days, beginning with a very strong
cold front Wednesday morning that will shift southeast winds
15 to 30 mph to west/northwest 25 to 40 mph with gusts to 60
mph, strongest in the Camas Prairie, south-central Idaho south
to the Nevada border, and Snake River Basin east of Mountain
Home. A High Wind Warning will be in effect in these areas
Wednesday during and after the front passes. Strong west winds
will be especially hazardous for travelers in high-profile
vehicles on north-south roads. All other parts of our CWA will
be under a Wind Advisory, through Wednesday morning in Oregon,
and through Wednesday afternoon in Idaho. Pcpn will be moderate
to heavy, as rain up to 8000 feet until the front passes, then
snow down to 4000 feet behind the front. Heavy rain in steep
terrain in Idaho north of the Snake Basin will likely cause
rock slides. Best to avoid the Banks-Lowman Road and similar
roads in steep terrain until at least noon Wednesday. The snow
level will continue to lower Wednesday night, and even the lower
valleys may get a dusting as pcpn ends. Then clearing, rapidly
calming, and colder Wednesday night. By 12Z Thursday the next
storm, in the form of a Pacific warm front moistened by another
atmospheric river, will spread snow across our CWA above 4000
feet, mainly in northern areas, prompting a Winter Storm Watch
for Thursday through Thursday evening in the West Central Idaho
Mountains, Boise Mountains, and Camas Prairie. In those areas
8 to 15 inches of snow may accumulate before the warm front
raises the snow level to 7000 feet late Thursday night. The
following cold front will change rain back to snow Friday
down to 6000 feet with further accumulation expected.

LONG TERM...Friday through Tuesday...An atmospheric river will
sag south across the area on Friday. A strong mid-level jet and
upslope flow will bring moderate to heavy precipitation to the
central Idaho mountains and much lighter amounts elsewhere. The
best chance of precipitation on Friday outside of the mountains
will be along a cold front that moves through on the back side
of the atmospheric river late in the day. Snow levels will be
5-7kft MSL on Friday, with heavy high mountain snow and rain at
lower elevations. Where precipitation in the mountains falls as
rain, rock slides will remain a concern. The strong jet will
also result in gusty surface winds, with gusts 30-50 mph across
the higher terrain, in SE Oregon, and SW Idaho south of the
Snake River. On Saturday, the front will stall near the Nevada
border but moisture transport will decrease, resulting in lower
precipitation chances. Snow levels Saturday will range from
around 3000 feet in the north to 6000 feet along the Nevada
border.

On Sunday and Monday, southwest flow aloft ahead of a deep trough
in the Gulf of Alaska will carry a plume of subtropical into
our area, bringing another round of widespread precipitation.
A warm front along the leading edge will push snow levels
higher once again, reaching 6-8kft by Sunday night. Moderate
to heavy precipitation totals are likely with this event, but
significant snowfall will be limited to the peaks. Strong
southwest flow aloft will continue to bring the heaviest totals
to the central Idaho mountains. Our area will remain under
southwest flow through Tuesday, keeping temperatures 10-15
degrees above normal through the period. However, by Tuesday
there is uncertainty in the evolution of the trough, with the
trough expected to elongate near the coast. If it deepens too
much, our area could be east of the precipitation bringing drier
and very mild conditions, but for now a 20-50% chance of rain
and snow will continue into Tuesday.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Wind Advisory from 5 AM to 5 PM MST Wednesday
     IDZ011-013-014-029.
     Winter Storm Watch from late Wednesday night through Thursday
     evening IDZ011-013-028.
     Wind Advisory from 5 AM to 11 AM MST Wednesday IDZ012-033.
     High Wind Warning from 8 AM to 5 PM MST Wednesday
     IDZ015-016-028-030.
OR...Wind Advisory from 5 AM MST /4 AM PST/ to 11 AM MST /10 AM
     PST/ Wednesday ORZ061>064.

&&

$$

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DISCUSSION...JM
AVIATION.....TL
SHORT TERM...LC
LONG TERM....ST