829
FXUS65 KBOI 172102
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
302 PM MDT Thu Sep 17 2026

.KEY MESSAGES...
- Upper low pressure approaching from ne California will bring
  showers, scattered strong thunderstorms, and cooler
  temperatures through Friday.

- Strongest thunderstorms in central Idaho with gusty outflow
  winds, hail, and brief heavy rain.

- Gradual warming and drying trend beginning Saturday and
  continuing through at least Tuesday.

&&

.SHORT TERM /Through Saturday Night/...
Southwesterly flow ahead of the approaching upper low will keep
temperatures warm across the region today, with dry air
preventing storm formation over the Treasure Valley and Owyhee
Mountains in Idaho and Malheur County in Oregon. Otherwise,
showers and thunderstorms are expected to return this afternoon
through evening over eastern OR and the west-central ID
mountains. Latest satellite imagery shows some clearing and
cumulus buildup over the aforementioned areas, aligning with the
expected instability for this evening. Gusty outflow winds up
to 50-60 mph, small hail, and brief heavy rain are the main
concerns. Abundant lightning is also likely with these scattered
storms in the afternoon, and fast storm motion will also keep
rainfall amounts low, especially over southeast Oregon. This
will increase the risk for lightning ignitions, prompting the
Red Flag Warning for scattered lightning through 9 PM MDT this
evening. Conditions will cool 5-10 degrees Friday as the low
pressure system moves overhead. Scattered showers and isolated
afternoon thunderstorms will occur again Friday, with increased
coverage over the Treasure Valley and Malheur County. Showers
will then taper off over the easternmost portions of the CWA on
Saturday with high pressure building back in over the region.

&&

.LONG TERM /Sunday through Thursday/...
High pressure rebuilding over the region will return a slight
warming and drying trend Sunday through Monday, with peak
daytime temperatures expected to hover in the lower 80s for the
Treasure Valley area. Late Monday through Tuesday, the area will
be sandwiched between a shortwave trough steering across the
lower Great Basin and a longwave Pacific trough moving into the
northwest coast. This pattern will keep us in moderated zonal
flow aloft on Tuesday, with seasonable conditions and a chance
of showers near the ID-NV border. Come Wednesday, the area will
come under a strong southwest flow ahead of the approaching
Pacific trough, continuing dry conditions and temperatures 5 to
10 degrees above normal through Thursday.

&&

.AVIATION /18Z Thursday through Friday/...
Issued 1043 AM MDT THU SEP 17 2026
VFR. Increasing clouds with isolated to scattered
showers/thunderstorms developing from south to north, primarily
near KTWF-KJER and KMYL-KBKE later after 20Z. Storms capable of
erratic outflows to 35 kt and small hail. Mountains obscured in
precipitation. Surface winds: Generally variable under 10 kt,
becoming S-SW 5-15 kt with gusts up to 25 kt in the later
afternoon. Winds aloft at 10kft MSL: E-SE 15-30 kt.

KBOI...VFR with few-scattered mid-high clouds this afternoon.
Surface winds: SW-SE 7-12 kt with gusts to around 20 kt,
becoming variable under 8 kt in the evening.

Weekend Outlook...Brief MVFR and mountain obscuration in
lingering showers/thunderstorms near KMYL and KTWF-KJER on
Saturday, with showers tapering off by midday. Expect VFR
conditions otherwise through Sunday with variable winds less
than 10 kt overnight and in high terrain and NW 5-15 kt in
valleys during the afternoon.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Red Flag Warning until 9 PM MDT this evening for IDZ403-421.
     Fire Weather Watch from late tonight through Friday evening
     for IDZ403-421-423-424-426.
OR...Red Flag Warning until 8 PM PDT this evening for ORZ670-671-
     674-675.
&&

$$

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SHORT TERM...JY/LC
LONG TERM....JY
AVIATION.....JY