788
FXUS65 KBOI 171133
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
533 AM MDT Thu Sep 17 2026

.UPDATE...Updated aviation discussion.

&&

.KEY MESSAGES...
- A low pressure system from southwestern Oregon will bring
  showers, scattered thunderstorms, and cooler temperatures
  Thursday through Friday.

- Some storms will be strong today, with gusty outflow winds,
  small hail, and brief heavy rain.

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

&&

.SHORT TERM /Through Saturday Night/...
Issued 318 AM MDT THU SEP 17 2026
Strong thunderstorms occurred over Twin Falls and Jerome
overnight, with gusts up to 59 mph reported along a strong gust
front near Twin Falls at 1230 AM. Warm southerly flow 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 will form early in the day over high
terrain in southwest Idaho and over the Blue Mountains in
Harney-Baker County, OR. These will strengthen as the low center
moves into northern Nevada with enhanced instability (500-1000
J/Kg of surface based CAPE) and shear of over 30 kts over high
terrain this afternoon. 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 Fire Weather Watches for
Idaho and Oregon zones. Conditions will cool by about 5-10
degrees as the low pressure system moves overhead tomorrow.
Scattered showers and isolated afternoon thunderstorms will
occur again tomorrow, with increased coverage over the Treasure
Valley and Malheur County. Showers will then taper off on
Saturday with high pressure building back in over the region.

&&

.LONG TERM /Sunday through Thursday/...
Issued 318 AM MDT THU SEP 17 2026
High pressure will bring a slight warming and drying trend to
the region through Tuesday. Temperatures will reach back to near
seasonal normals, with highs in the low 80s for the Boise area on
Monday. By late Tuesday, the Intermountain West remains sandwiched
between a deep low pressure system over the eastern Pacific and
a weakening low pressure system moving onshore in southern
California. This will keep us in moderated zonal flow aloft on
Tuesday, with seasonable conditions and a chance of showers near
the ID-NV border. High pressure then looks to build in sharply
over the region as the low over the Pacific deepens. This would
bring southerly flow, keeping temperatures about 5-10 degrees
above normal on Wednesday and Thursday.

&&

.AVIATION /12Z Thursday through Friday/...
Issued 531 AM MDT THU SEP 17 2026

VFR. Increasing clouds with showers and isolated thunder
developing moving from south to north, primarily near KTWF-KJER
and near KMYL- KBKE later. Storms capable of erratic outflows to
35 kt and small hail. Mountains obscured in precipitation.
Surface winds: Generally variable up to 10 kt overnight.
Becoming S-SW 5-15 kt with gusts up to 25 kt early Thu/PM. Winds
aloft at 10kft MSL: E-SE 15-30 kt.

KBOI...VFR. A 10-15% chance of showers early Thu/AM into Thu/PM.
Surface winds: NW under 10 kt this evening. Becoming SW-SE 7-12 kt
with gusts to around 20 kt late Thu/AM.

Weekend Outlook...Brief MVFR and mountain obscuration in
lingering showers near 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 from noon today to 9 PM MDT this evening for
     IDZ403-421.
OR...Red Flag Warning from 11 AM this morning to 8 PM PDT this
     evening for ORZ670-671-674-675.
&&

$$

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AVIATION.....SA
SHORT TERM...SA
LONG TERM....SA