510
FXUS65 KBOI 160407
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
907 PM MST Mon Dec 15 2025

.DISCUSSION...Scattered to broken high clouds are currently
present tonight, associated with the weak system that passed
through earlier today. The later-than-expected arrival of this
system kept afternoon temperatures cooler. Clouds will persist
across the forecast area into Tuesday, which should help
maintain mild overnight temperatures, though they have been
adjusted a few degrees lower to match the latest observed
trends. Warm and dry conditions are expected through much of
Tuesday under mostly cloudy skies.

A much stronger, more moist system remains on track for early
Wednesday, which will bring breezy conditions and widespread
precipitation favoring the Central Idaho Mountains. Due to
persistently high snow levels (above 7,000 feet for most of the
event), areas below 7,000 feet are likely to see moderate
rainfall, totaling 0.50 to 1.00 inch. Strong westerly flow aloft
will create a rain-shadowing effect on the Treasure Valley,
limiting total precipitation to around 0.10 inches. While the
upper-level jet maximum reaches the area early Wednesday morning
and moves quickly into eastern Idaho by late afternoon, which
is a slightly less optimal timing for high winds, it remains
strong enough to produce widespread winds of 25 to 35 MPH with
gusts up to 55 MPH. More favorable areas for stronger winds look
to be the Steens Mountains, the higher terrain of the Owyhee
Mountains/Southern Highlands, and the Camas Prairie, where
sustained winds of 30 to 40 MPH with gusts up to 65 MPH. Based
on this guidance, the High Wind Watch has been updated to a Wind
Advisory for most areas, while a High Wind Warning has been
issued for the Camas Prairie, with a 70% probability of wind
gusts exceeding 55 MPH. The updated forecast will be issued
shortly.

&&

.AVIATION...Mostly VFR with periods of low VFR or MVFR in
scattered rain/snow showers tonight. Showers in the Snake Plain
could produce moderate rainfall, mainly near the Magic Valley.
IFR-LIFR in mountains due to lower ceilings and mountain
obscuration. Snow levels remain around 7-8 kft MSL through the
period, lower to the north. Areas of LLWS continue especially in
SE OR. Surface winds: SE- SW 5-15 kt with gusts to 25 kt in SE
OR and ID/NV border. Winds aloft at 10kft MSL: W 25-45 kt.

KBOI...VFR. A 15-30% chance of rain showers tonight/early tomorrow
morning. Surface winds variable, but generally SE 4-10 kt

&&

.AIR STAGNATION...The system today wasn`t strong enough to
remove the inversion as evident on the 00z Boise sounding.
However, increasing winds on Tuesday as the next system
approaches should be enough to break the inversion late Tuesday.
An active pattern will continue through the remainder of the
weak bringing increased mixing and winds, as well as widespread
precipitation, Tuesday and Wednesday which will end the stagnant
conditions.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Wednesday night...At 2 PM MST a
weak cold front was in western ID with a band of light rain
extending north-south along the OR/ID border. The front was
moving steadily east with slightly more pcpn than models
predicted but should total less than .15 inch even in the
wettest locations. The front will stir up the stagnant air
but not enough to end the Air Stagnation Advisory which will
continue until 5 AM Tuesday. Clouds and light winds will
moderate low temps tonight, and increasing southeast winds
will boost max temps to near record highs Tuesday. Tuesday
night will be windy and very mild ahead of a very strong
Pacific cold front due in the pre-dawn hours Wednesday in OR,
and early Wednesday morning in western ID. South/southeast
winds will shift abruptly to west/northwest as the front passes
and increase to 30 to 40 mph with possible gusts as high as 60
mph in southern zones. A High Wind Watch has been issued in
those zones (listed below) for Wednesday morning in OR and
through 2 PM MST Wednesday afternoon in western ID. Strongest
winds are expected in the western Magic Valley and Camas
Prairie. Pcpn will be heavier with the strong cold front with
greatest amounts (near 1.00 inch) in eastern Valley County and
northern Elmore County in ID late Tuesday night through late
Wednesday night. Heaviest pcpn will fall as the cold front
passes and may result in rock slides in steep terrain. Travelers
would be wise to avoid the Banks-Lowman road in ID and be wary
on ID state highway 21 northeast of Idaho City. The rest of ID
north of the Snake Basin should have .25 to .50 inch liquid
equivalent, while southern areas including the Snake Basin
receive .10 to .25 inch, with similar amounts in eastern OR. The
snow level will lower rapidly to valley floors later Wednesday
in northern zones and to near 5000 feet in southern zones.
Snowfall 3 to 6 inches is expected in the higher ID mountains
late Wednesday through Wednesday evening. Wednesday night
should be calming, drying, and significantly cooling.

LONG TERM...Thursday through Monday...Precipitation chances
continue through the extended, with a hefty push during Thursday,
Friday, and early Saturday. This comes as another atmospheric river
event impacts the Pacific NW from an elongated disturbance, courtesy
of the Gulf of Alaska low. A strong, westerly mid-level jet will
accompany this disturbance. As a result, this system will pull
in a long fetch of considerable subtropical moisture, spreading
moderate/heavy precipitation into the area. Snow levels will
oscillate quite a bit during this period, associated with the
tight temperature gradient, making snowfall accumulations a
significant forecast challenge during this period. Overall,
snow levels are expected to be lowest across the north,
gradually rising from south to north throughout the day
Thursday. Snow levels will then gradually lower from north
to south as a cold front moves in late Friday/early Saturday.
Overall, mountains could see 1 to 2 inches of liquid equivalent
throughout this period, along with snowfall totals 1 to 2 feet
at the ridgetops (depending heavily on the snow level). The
period of rainfall over saturated, steep terrain will also
introduce rockslide concerns.

In addition to precipitation, strong surface winds are expected
to develop across much of the area, particularly Friday, ahead
of/along the cold front. Gusts will be strongest across southeast
Oregon, the ID/NV border, and the mountains of southwest Idaho.
Meanwhile, temperatures are forecast to stay above normal
Thursday and Friday, with the coldest air expected across
west-central/central Idaho and eastern Oregon.

Once the aforementioned system exits, there will be a brief
respite from precipitation late Saturday into Sunday morning.
This will occur before yet another push of precipitation comes
ahead of a upper-level long wave trough slowly moving inland
Sunday and Monday. Models currently disagree on how much of the
polar air to the north will penetrate E Oregon and SW Idaho,
resulting in poor forecast confidence on temperatures and snow
levels this far out. Regardless, ample moisture will yield a
new round of notable precipitation amounts for the area, with
upslope flow favoring the mountains of west-central/central
Idaho once again.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Air Stagnation Advisory until 5 AM MST Tuesday
     IDZ011>014-016-028-033.
     Wind Advisory from 5 AM to 5 PM MST Wednesday
     IDZ014>016-029-030.
     High Wind Warning from 11 AM to 5 PM MST Wednesday IDZ028.
OR...Air Stagnation Advisory until 5 AM MST /4 AM PST/ Tuesday
     ORZ061>064.
     Wind Advisory from 5 AM MST /4 AM PST/ to 11 AM MST /10 AM
     PST/ Wednesday ORZ061>063.

&&

$$

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DISCUSSION...JDS
AVIATION.....JM
AIR STAGNATION...JDS
SHORT TERM...LC
LONG TERM....CH