textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Isolated afternoon thunderstorms Wednesday, mainly forming over the Idaho mountains, and southern Twin Falls County on Thursday afternoon.

- Scattered showers and thunderstorms over southwest Idaho on Friday and Saturday. Some of the storms may be severe.

SHORT TERM /Through Friday Night/

Issued 205 PM MDT TUE AUG 25 2026 A seasonably strong anticyclone over Arizona and New Mexico is dominating the synoptic pattern over the western CONUS, leaving the interior Northwest in broad and strengthening southwest flow aloft. This also means warm temperatures will continue with little day-to-day change through Thursday. The primary concerns will revolve around the potential for thunderstorms each afternoon, and then increasing winds with low humidity by Thursday. Thunderstorms are most likely near the Nevada border into the western Magic Valley both this afternoon and Wednesday afternoon, with strong gusty winds the primary threat. Isolated thunderstorms are still possible over the central Idaho mountains as well. Drier air will limit any thunderstorm potential over eastern Oregon, including Malheur/Harney and the Oregon Outback, with only low probabilities existing over Baker County. By Thursday, the increase in southwest flow aloft associated with a strengthening trough ejecting eastward across Oregon will bring gusty winds to southeast Oregon and far southwest Idaho. This will combine with the antecedent low RH/dry conditions and warm temperatures to create an elevated wind-driven fire weather threat across these areas.

LONG TERM /Saturday through Wednesday/

Issued 205 PM MDT TUE AUG 25 2026 drop temperatures down to near normal. Ahead of this cold front, Tropical Storm Iselle will weaken, with its remnant moisture transported over our area in southwesterly flow aloft. As the long range ensemble guidance sees it, PWAT values across southwest Idaho will increase to around the 95th percentile of climatology (highest near the Magic Valley and eastward). The timing of the cold front and moisture advection right now looks favorable for the development of showers and thunderstorms come Friday afternoon, mainly in SW Idaho and the southeastern portions of the Great Sandy Desert. With high PWATs, heavy rain will be a hazard with storms that develop and the flash flood risk will need to be monitored.

The cold front and associated upper trough will be quick to push the moisture off to the east come Saturday. The weekend will feature generally dry conditions with temperatures at or below normal. Come Monday/Tuesday, another trough digging down the coast of British Columbia and grazing our area will bring a slight chance of precipitation across higher terrain of southwest Idaho. This fall- like transition pattern looks to continue beyond the long-term period, with the extended outlooks leaning towards above normal precipitation and below normal temperatures.&&

AVIATION /06Z Wednesday through Thursday/

Issued 1221 AM MDT WED AUG 26 2026 VFR. Virga during morning hours. Then, isolated showers and thunderstorms near KTWF/KJER and over central ID mtns in the afternoon/eve. Outflows 30-45 kt. High density altitude in the afternoon due to heat. Areas of smoke near wildfires degrading visibility. Surface winds: variable 5-12 kt, then mainly SW-SE 5-15 kt with gusts around 20 kt in the afternoon. Winds aloft at 10kft MSL: SW 10-25 kt.

KBOI...VFR. Virga overnight through Wed afternoon. High density altitude in the afternoon. Surface winds: SE 5-15 kt.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Fire Weather Watch from Thursday afternoon through Thursday evening for IDZ423. OR...Fire Weather Watch from Thursday morning through Thursday evening for ORZ670>672. Air Quality Alert until noon PDT Wednesday for ORZ062.