textproduct: Boise

KEY MESSAGES

- Heat Advisory continued through Friday in the Treasure Valley, western Magic Valley, and Upper Weiser River Valley.

- Increased chance of afternoon and evening showers and thunderstorms over higher terrain Friday through Sunday.

- Above normal temperatures next week with a chance of afternoon thunderstorms over southwest Idaho Monday and Tuesday.

SHORT TERM /Through Saturday Night/

The Heat Advisory for the Treasure Valley, western Magic Valley, and Upper Weiser River Valley will continue through Friday as a high-amplitude upper ridge holds strong over the Four Corners region. Models bring monsoon moisture northward through NV Friday leading to a 15-25 percent chance of high-based thunderstorms on the Idaho side late Friday through Saturday. These storms would bring gusty winds but little rain. Meanwhile, satellite shows high clouds streaming into our CWA from the Pacific subtropics guided by an upper trough off the west coast. These clouds won't bring rain but they should lower Friday afternoon's temperatures a few degrees. Without the clouds the lower valleys would get close to 105 degrees, and a couple of models actually show that. On Saturday, deeper monsoon moisture from the south will allow thunderstorms to be more effective rain-producers, while continuing cloudiness and the approach of a weak surface cold front and the coastal upper trough should lower temps 5 to 10 degrees from Friday's highs.

LONG TERM /Sunday through Thursday/

Sunday will be a bit cooler than Saturday, but still warm or hot across the region, with relative humidities still very low in the drier airmass. Frontal winds on Sunday move into central Idaho, bringing 20 to 30 mph wind gusts to higher terrain in the afternoon. Winds return to normal strength through the rest of next week. As the upper ridge builds back in following the front and trough, temperatures slowly climb into next week, but hold steady around normal to a few degrees above normal for this time of year. The building ridge also allows for monsoonal moisture to continue to stream into the region, leading to a daily slight chance of showers and storms in s-central Idaho and central Idaho.

AVIATION /18Z Thursday through Friday/

Issued 1130 AM MDT THU AUG 20 2026 VFR. Increasing clouds AOA 15 kft MSL. Some reduction in visibility due to wildfire smoke. Isolated high-based showers/storms near the ID/NV border 20/21Z - 21/01Z. Surface winds: SW-NW 5-15 kt until 21/01Z then variable less than 8 kt. Winds aloft at 10kft MSL: SW 15-25 kt.

KBOI...VFR, Increasing high clouds AOA 18 kft MSL. Some reduction in visibility due to wildfire smoke. Light diurnal surface winds through Friday.

Weekend Outlook...Scattered showers and thunderstorms late Friday through Saturday. Gusty outflow winds and locally heavy rain in storms. Drier Sunday. Local reductions in visibility due to wildfire smoke through the weekend. Gusty SW winds Saturday across SE Oregon. Breezy W-NW winds all areas on Sunday.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Heat Advisory until 9 PM MDT Friday for IDZ012-014-016-033. OR...Heat Advisory until 9 PM MDT /8 PM PDT/ Friday for ORZ064. Fire Weather Watch from Saturday afternoon through Saturday evening for ORZ670>672.