456
FXUS65 KBOI 120543
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
1143 PM MDT Fri Sep 11 2026

.UPDATE...Updated aviation discussion.

&&

.KEY MESSAGES...
- Warm and mostly dry today and tomorrow ahead of a strong cold
  front late tomorrow night with scattered showers, isolated
  thunderstorms, high elevation snow, and gusty westerly winds.

- Breezy and much cooler Sunday, with lingering showers in
  northeast OR and the central ID mountains.

- Unsettled cool conditions through next Wednesday, then a
  warming and drying trend likely for the end of the week.

&&

.SHORT TERM /Through Sunday Night/...
Issued 209 PM MDT FRI SEP 11 2026
Warm and dry tonight under a weak trough. A strong Pacific
upper low is currently tracking toward the Northwest coast and
is expected to reach the coast Saturday afternoon. Recent model
guidance has continued the trend of a slower low progression as
well as nudged the core of the upper level low further north as
it tracks inland overnight Saturday into Sunday. Ahead of this
system on Saturday, strong southwesterly flow aloft will tap
into warm air and push high temperatures back up near 5 to 8
degrees above seasonal averages. However, the slower timing will
delay the precipitation to late Saturday evening. Pre-frontal
pressure gradients will produce gusty southwesterly surface
winds, gusting 35 to 45 mph across southeast Oregon and the
Snake River Plain down to the Nevada border. In addition to the
warmth, southwesterly upper level wind looks to transport a
layer of wildfire smoke northeastward from fires in California,
leading to increasing haziness across southeast Oregon and
southwest Idaho through Saturday afternoon.

The primary cold front will push west-to-east across the area
late Saturday evening with showers and thunderstorms possible
north of a Rome-Ontario-Stanley line into Sunday morning.
Instability is marginal at best but enough to warrant a slight
chance for thunderstorms overnight. The best chance for showers
and thunderstorms will be largely focused across Baker County in
Oregon and central Idaho north of the Snake River Basin.

The cold front crosses southwest Idaho Sunday morning continuing
the windy conditions across much of the area into Sunday
afternoon. Temperatures will plummet roughly 15 to 20 degrees
below Saturday highs. Showers linger across the northern and
eastern mountain zones Sunday morning before tapering off Sunday
afternoon. Snow levels will drop to 7000 to 8000 feet MSL,
bringing light snow accumulations to the high mountain peaks.
Clearing skies Sunday night and lighter winds will support rapid
radiational cooling, leading to a cold night area-wide and
potential patchy valley fog early Monday morning.

&&

.LONG TERM /Monday through Friday/...
Issued 209 PM MDT FRI SEP 11 2026
As the low pressure system from the weekend moves eastward,
troughing continues along the west coast. The troughing will bring
southwesterly flow and eventually strengthen into a closed low that
rejoins the broader flow later in the week. The period from Monday
through Wednesday will see steadily warming temperatures as the
trough and low build. There is a very low chance of showers over
high terrain during this time frame as the closed low blocks the
bulk of Pacific moisture from reaching the area. Models have shown
little run to run consistency on the track of the closed low as it
becomes a longwave trough later in the week. A high amplitude ridge
follows closely behind, threatening to continue warming conditions
with drier weather if the trough misses us. However, the latest runs
of long range models show the trough bringing us higher chances for
precipitation Thursday and Friday.

&&

.AVIATION /06Z Saturday through Sunday/...
Issued 1138 PM MDT FRI SEP 11 2026

VFR through Saturday. Cold front arrives this evening with
increasing showers across E Oregon and w-central ID. A 10%
chance of lightning. Localized MVFR and mountain obscuration in
showers. Surface winds: variable up to 10 kt. Then, SE-SW 5-15
kt this afternoon, with gusts to 25-30 kt in E Oregon and
Owyhee Mountains. Winds aloft at 10kft MSL: W-SW 15-30 kt.

KBOI...VFR. Surface winds: SE 5-12 kt. Shifting to gusty SW-NW
tonight with cold front.

Sunday Outlook...Generally VFR. Showers and 10% chance of
lightning across E Oregon and w-central Idaho Sunday morning,
and again Sunday afternoon. Localized MVFR and mountain
obscuration in showers. Patchy mountain valley fog Sunday
morning. Snow levels 6500-7500 ft MSL by Sunday morning. Surface
winds Sunday: SW-NW 5-15 kt, with PM gusts around 20-25 kt.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Red Flag Warning from noon to 9 PM MDT Saturday for IDZ423-426.
OR...None.

&&

$$

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AVIATION.....SA
SHORT TERM...JDS
LONG TERM....JM