textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- A 15 to 20 percent chance of thunderstorms near the Idaho/Nevada border this afternoon.

- Showers and thunderstorms increasing in coverage Thursday, continuing through Saturday. - Fire weather concerns increase due to threat of thunderstorms Thursday afternoon through Friday.

- Temperatures cooling to around 5 degrees below normal come Friday.

SHORT TERM /Through Friday Night/

Issued 249 AM MDT WED AUG 12 2026 Today will be the last day of warm and dry conditions before a pattern change come Thursday; barring a slight chance of showers and thunderstorms (15-25% chance) in far southern Twin Falls county this afternoon. High temperatures this afternoon will rise to generally 85-95 degrees across lower elevations and the high desert. Come Thursday, troughing over the Pacific Northwest, aided by an ejecting shortwave, will offer increasing chances of showers and thunderstorms. The aforementioned shortwave is progged to cross over the eastern portion of our CWA, giving way to the best chances of precipitation (30-50%) falling near the ID/NV border and Central ID Mountains come Thursday afternoon/evening. Weak instability Thursday afternoon (limited by increased cloud cover) will allow for a 15-25% chance of thunderstorms in the same areas mentioned above. With this being the initial push of monsoonal moisture, the boundary layer will still be dry, allowing for gusty winds and lightning to be the primary hazard with Thursday afternoon storms. The drier nature of this initial wave is also leading to elevated fire weather concerns. Scattered showers will continue through Friday across SW Idaho and far eastern Oregon. Continued moistening will allow for some weak elevated instability to remain overnight Thursday, so some nocturnal thunder can't be ruled out.

The best chances of precipitation (at least across southwest Idaho) will come Friday, with LREF mean PWAT values ranging from the 85-95th percentile. As has been the trend, the ID/NV border and central ID mountains will have the highest odds of precip, with a 60-90% chance. With the atmosphere becoming more saturated at this point, the main hazard will transition from gusty winds into heavy rain. Recently burned areas and steep/rocky terrain will be most susceptible flooding and debris flows with any heavy rain that does occur. Also... temperatures will be around 5 degrees below normal come Friday.

LONG TERM /Saturday through Wednesday/

Issued 249 AM MDT WED AUG 12 2026 Scattered showers and isolated to scattered thunderstorms will continue Saturday as another shortwave passes over in the flow aloft. With PWATS remaining around the 90th percentile (as the LREF mean sees it), the hazards mentioned in the short-term Friday will also carry over into Saturday. A warming and drying trend will set in to start the coming week as ridging builds into the intermountain west. Isolated afternoon showers and thunderstorms (10-20% chance) will persist across higher terrain into the start of the week. By mid-week, A low approaching from the west will lead to increasing precipitation chances and a cooling trend yet again.

AVIATION /12Z Wednesday through Thursday/

Issued 438 AM MDT WED AUG 12 2026

Generally VFR with some periods of MVFR possible in wildfire smoke. A 15-20% chance of showers and thunderstorms south of KTWF this afternoon. High density altitude this afternoon due to heat. Surface winds: Variable under 10 kt this morning. Becoming W-NW 10-20 kt this afternoon. Winds aloft at 10kft MSL: W-SW 5-15 kt.

KBOI...VFR with reduction in visibility due to wildfire smoke at times. Foothills obscured by smoke.. High density altitude this afternoon due to heat. Surface winds: light and variable this morning, becoming NW 7-12 kt with gusts up to 18 kt in the afternoon.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Air Quality Alert until 1 PM MDT this afternoon for IDZ011-012- 014-015-029-033. Fire Weather Watch from Thursday afternoon through late Thursday night for IDZ400>403-420-421-423-424-426. OR...Fire Weather Watch from Thursday afternoon through late Thursday night for ORZ672>674. Air Quality Alert until 11 AM PDT this morning for ORZ061.