textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Fire weather risk continues due to thunderstorm activity today.

- Thunderstorms could bring outflow winds up to 50 mph. In addition, heavy rain may also increase the risk for flash flooding, especially for vulnerable burn scars today.

- Temperatures near normal through Tuesday, then a few degrees of warming expected by late week.

SHORT TERM /Through Monday Night/

Issued 208 PM MDT SAT AUG 15 2026 Strong thunderstorms are continuing to develop across the area bringing heavy rain, small hail and gusty outflow winds to 50 mph. Despite the storms producing rainfall, lightning fire starts are still a risk especially across the lower terrain. High confidence (40% chance) in thunderstorms moving through the Treasure Valley between 3 PM and 6 PM bringing brief heavy rain, lightning and wind gusts up to 50 mph. Increased risk for flash flooding on the recent burn scars especially the Wapiti remains elevated through this evening. Please monitor the latest weather information if you live or are traveling near the large burn scars.

Convective activity will taper off late tonight as diurnal cooling takes over and the primary shortwave exits to the northeast. On Sunday, an upper level ridge builds over the Great Basin, initiating an overall drying and warming trend. Moisture will be significantly limited compared to Saturday, though leftover instability will keep a slight chance (15 to 25 percent) of afternoon showers and thunderstorms over the higher terrain of central and south-central Idaho. High temperatures on Sunday will rebound to around 2 to 5 degrees above normal across the lower valleys.

By Monday, residual monsoonal moisture around the western periphery of the ridge will lead to an increase in mid-level cloud cover and an expanding threat of afternoon and evening showers and thunderstorms. The best coverage on Monday will be focused over the higher terrain of northeast Oregon and central/south-central Idaho, though isolated storms cannot be ruled out for lower elevation valleys. Gusty erratic winds and localized heavy downpours will once again be the main threats with storm development on Monday. Temperatures Monday night will remain mild, staying in the upper 50s and 60s for low elevations.

LONG TERM /Tuesday through Saturday/

Issued 208 PM MDT SAT AUG 15 2026 An upper-level shortwave trough will continue to move east through the Pacific Northwest and Northern Rockies Tuesday and early Wednesday. Shower and thunderstorm chances will be limited to the higher terrain of central Idaho as this passes through. This disturbance will suppress the upper-level ridge building in the Great Basin on these days, however Wednesday afternoon onward the ridge will amplify over the area. As the Desert Southwest ridge builds, southwesterly flow aloft will overspread the region, increasing temperatures and moisture gradually late week. Additionally, models agree on a Pacific low pressure system slowly moving onshore late week going into the weekend. This pattern will support the influx of monsoonal moisture once again, with shower and thunderstorm chances increasing by Friday and further Saturday.

AVIATION /00Z Sunday through Monday/

Issued 528 PM MDT SAT AUG 15 2026 Scattered showers and thunderstorms through the late evening, especially north and east of the Snake Plain and through the Magic Valley of Idaho. Heavy rainfall, small hail, and wind gusts to 40-45 mph with the strongest storms. Brief reductions in visibility in blowing dust possible as well this evening. Surface winds variable around 10 kt, except vrb 30g40 kt near thunderstorms. Light diurnal winds overnight, favoring an ESE direction. Winds aloft at 10kft: SW 10-20 kt.

KBOI...Showers moving to the northeast of the terminal by 01Z, with lingering gust front winds around 20-25 kt. Drying with diurnal SE winds developing this evening less than 10 kt.

Sunday Outlook...VFR area-wide with isolated showers/thunderstorms across central/south-central Idaho in the afternoon and evening. Brief MVFR/IFR possible along with gusty winds near thunderstorms. Winds less than 10 kt elsewhere, along with areas of smoke near KBKE/KBNO.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Red Flag Warning until 9 PM MDT this evening for IDZ400-420- 423-424-426. Flash Flood Watch until 9 PM MDT this evening for IDZ013. OR...Red Flag Warning until 9 PM MDT /8 PM PDT/ this evening for ORZ672>675.