textproduct: Boise

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 /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. OR...Red Flag Warning until 8 PM PDT this evening for ORZ670-671- 674-675.