textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Warm, dry, and smoky through Wednesday.

- Around a 10 to 15 percent chance of thunderstorms near the Idaho/Nevada border on this afternoon and Wednesday afternoon.

- Monsoon moisture arrives Thursday afternoon ahead of an upper level trough. - Fire weather concerns increase due to threat of thunderstorms Thursday afternoon through Friday.

SHORT TERM /Through Thursday Night/

Issued 231 PM MDT TUE AUG 11 2026 Warm and dry weather will continue through Wednesday with a slight (15 percent chance) of thunderstorms near the southern Idaho border this afternoon and again on Wednesday afternoon. Poor air quality due to wildfire smoke continues to be an issue as well. Recent upper air soundings indicate better mixing condition each afternoon, but nighttime surface based temperature inversions will cap mixing and allow smoke to settle thickly into most valley locations again overnight. Monsoon moisture will arrive on Thursday afternoon increasing the threat of thunderstorms and raising fire weather concerns. Forecast model soundings show enough mid-level moisture to fuel thunderstorms producing lightning as early as Thursday afternoon. Lower levels of the atmosphere are expected to remain dry initially, which will limit rainfall potential and increase risk of new fire starts due to lightning.

LONG TERM /Friday through Tuesday/

Issued 231 PM MDT TUE AUG 11 2026 Southwest flow aloft will continue to bring substantial monsoon moisture to most of the area on Friday. Forecast precipitable water values are near the 80th-90th percentile of normal, indicating a high potential for heavy rainfall in any showers/thunderstorms that form. The best chance looks to be near the Nevada border and high terrain in the Central Idaho Mountains with a 50-70% chance of precipitation and a 20-30% chance of thunderstorms on Friday and Saturday. With any heavy rainfall that does occur, burn scars and steep/rocky terrain will be susceptible to flash flooding and debris flows. Gusty outflow winds up to 35 mph, lightning, and heavy rain are the main hazards with these storms. Cooler temperatures will also accompany this push of moisture, with high temperatures about 5-10 degrees below normal on Friday and Saturday.

A ridge of high pressure will build back into the region early Sunday, with lingering moisture keeping a 10-20% chance of precipitation over higher terrain through Monday. A brief warming and drying trend will occur on Sunday and Monday ahead of another push of showers and thunderstorms with a quick moving low late Tuesday.

AVIATION /00Z Wednesday through Thursday/

Issued 547 PM MDT TUE AUG 11 2026

Generally VFR with periods of MVFR conditions in wildfire smoke. Mtn obscuration in smoke. High density altitude due to heat tomorrow afternoon. Surface winds: W-NW 5-15 kt through early evening, then generally variable under 10 kt overnight. Winds aloft at 10kft MSL: W-SW 5-15 kt.

KBOI...VFR with reduction in visibility due to wildfire smoke at times. Foothills north of KBOI will be obscured by smoke. High density altitude tomorrow afternoon due to heat. Surface winds: NW 6-12 kt through early evening, becoming light and variable overnight.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Air Quality Alert until 1 PM MDT Wednesday 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 Wednesday for ORZ061.