textproduct: Boise

KEY MESSAGES

- Numerous showers and thunderstorms today across the central Idaho mountains. Thunderstorms may produce heavy rain, creating a risk of flash flooding and debris flows, especially over burn scars and steep terrain.

- Isolated to scattered showers and thunderstorms elsewhere today and Thursday, with brief heavy rain and gusty winds possible.

- Areas of smoke will continue through the week.

- Very hot, dry, and breezy to end the week.

SHORT TERM /Through Friday Night/

An upper level ridge centered across the south-central U.S. and extending into the Pacific Northwest, combined with a trough off the coast, will continue to transport monsoonal moisture across the area under southerly flow. A shortwave impulse will lift north out of Nevada bringing scattered showers to southwest Idaho this morning. This afternoon, the wave will move into central Idaho, producing numerous showers and thunderstorms over the mountains. Thunderstorms will be capable of producing heavy rain, creating a risk of flash flooding and debris flows, especially over burn scars and steep terrain. A Flash Flood Watch remains in effect for the Wapiti burn area this afternoon and early evening. Additionally, there will be enough instability for isolated to scattered showers and thunderstorms across most of southeast Oregon and the higher terrain south of the Snake River in southwest Idaho. Heavy rain will be possible in stronger storms with gusts to 45 mph. Most lower elevations will see a less than 20% chance of showers and thunderstorms today. Temperatures will be slightly lower today due to increased cloud cover and precipitation. Areas of smoke from regional wildfires will persist today, especially across east- central Oregon and west-central Idaho into the Treasure Valley.

On Thursday, the flow aloft will turn southwesterly as the ridge axis starts to move east, pushing deeper monsoonal moisture out of the area. However, a weak impulse ahead of the trough off the coast will bring a 10-30% chance of showers and thunderstorms to eastern Oregon and western Idaho in the afternoon and evening. Instability will extend into the lower elevations, bringing a better chance for thunderstorms to reach the Treasure Valley than previous days. Storms will be capable of gusty winds. Otherwise, southwest flow will bring hotter temperatures with lower valleys forecast to reach just over 100 degrees. Winds will become breezy in southeast Oregon. This trend will continue into Friday as gusts 20-35 mph overspread the higher elevations. Temperatures will be very hot with lower valleys approaching 105 degrees. Much drier air will arrive from the west, limiting thunderstorm potential to south-central Idaho and increasing fire weather concerns. Southwest flow aloft will transport some of the smoke away from the area, but drainage winds each night will continue to bring smoke impacts to some areas.

LONG TERM /Saturday through Wednesday/

A hot, dry, and breezy pattern will continue through the extended as southwest flow aloft persists between upper troughing along/off the coast and an upper ridge over the south- central U.S. Highs Saturday will remain very hot, forecast to exceed 100 degrees once again in the lower valleys. Winds will increase further ahead of a trough moving into western Washington, with widespread gusts 20-35 mph, strongest over higher terrain. Additionally, relative humidity will be very low resulting in elevated fire weather concerns. The trough will bring a slight cooldown Sunday into early next week, but it will still be hot and dry with lower valleys reaching the mid 90s. Winds will subside after Saturday, but it will still be breezy each afternoon. Dry air will keep shower and thunderstorm chances less than 10%.

AVIATION /06Z Wednesday through Thursday/

Issued 1227 AM MDT WED JUL 22 2026 Generally VFR, with areas of MVFR/IFR due to wildfire smoke. Visibility will be at a minimum overnight, with improvement during the peak of daytime heating. Showers and thunderstorms will be possible this evening and overnight near the Nevada border, with more widespread activity Wednesday afternoon. High density altitude due to continued hot temperatures. Thunderstorms Wednesday afternoon could bring torrential rain, wind gusts to 40 kt and terrain obscuration. The most likely impacted area will be in central Idaho. Surface winds: variable less than 10 kt overnight becoming WNW 10-15 kt after 20Z. Winds aloft at 10kft MSL: WSW around 10 kt.

KBOI...VFR with mid/high clouds, then visibility reductions due to wildfire smoke overnight into early Wednesday. High density altitude Wednesday afternoon. Showers will try to make it to the terminal Wednesday afternoon, and there is potential for gusty outflow winds Wednesday evening. Surface winds: variable less than 10 kt overnight becoming WNW around 10 kt after 20Z. Swinging back to the WNW Wednesday afternoon.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Air Quality Alert until 3 PM MDT this afternoon for IDZ011-012- 014-033. Flash Flood Watch from noon MDT today through this evening for IDZ013. OR...Air Quality Alert until 1 PM MDT /noon PDT/ this afternoon for ORZ061>064.