textproduct: Boise

KEY MESSAGES

- Scattered showers and isolated thunderstorms Friday and Saturday. Stronger storms possible in SE Oregon on Friday and SW Idaho on Saturday.

- Notable temperature swings from Sunday through next week with Monday and and Tuesday being the warmest days.

- A deeper low pressure system expected later next week for cold and wetter conditions.

SHORT TERM /Through Sunday Night/

An upper level trough situated off the Pacific Northwest coast continues to stream elevated moisture into the region. Mainly virga has been seen thus far across southwest Idaho and southeast Oregon this morning as the boundary layer remains quite dry still. Clouds cover should limit surface based instability this afternoon. The exception will be where mid level moisture will overlap with surface warming to support localized thunderstorm development, especially over southern Harney and Malheur counties as well as higher terrain in southwest Idaho. Inverted V atmospheric profiles will promote erratic, gusty outflow winds with any robust cell that develops. Rainfall becomes more likely by sunset as the PWs across the area approach the 95th percentile.

Precipitation chances exit southeast Oregon Friday night as moisture shifts eastward into southeast Idaho. On Saturday, the main upper level trough moves closer to the region, providing stronger synoptic forcing. A relatively well mixed boundary layer with enhanced instability and a strong upper level jet aloft should support scattered thunderstorm development and bring the potential for stronger downdrafts, leading to gusty outflow winds up to 45 to 55 mph with the strongest storms. Brief heavy rain is also possible given the high PWs though storms will be moving quite fast given the flow aloft lowering the risk of flash flooding. The best potential for thunderstorms is forecast across south-central Idaho Saturday afternoon.

A cold front pushes through the forecast area late Saturday evening, bringing drier air and ending convective activity overnight. Temperatures on Sunday will drop significantly behind the front, cooling to around 10 degrees below seasonal normals under breezy westerly winds.

LONG TERM /Monday through Friday/

Temperatures rebound closer to seasonal averages on Monday as shortwave ridging briefly takes hold. By Monday evening, the next trough begins moving inland from the coast and may pull monsoon moisture northward, supporting shower and thunderstorm chances primarily across south central Idaho. This trough will move across the Pacific Northwest Tuesday into Wednesday bringing a threat for showers and thunderstorms across the higher terrain. This feature will track ahead of a deeper low pressure system set to move into the Pacific Northwest coast late in the week. Consequently, expect enhanced cloud cover, intermittent shower and thunderstorm potential over higher terrain, and a tightening surface pressure gradient. Stronger, breezy surface winds are likely heading into Thursday and Friday along with another cooling trend. Ensemble spread remains slightly elevated regarding exact timing, but the overall signal favors a cool, windy, and unsettled end to the extended period.

AVIATION /06Z Friday through Saturday/

Issued 1220 AM MDT FRI AUG 28 2026 Mainly VFR. Light rain and virga will increase overnight into Friday across S Idaho and far SE Oregon. Isolated embedded thunderstorms will also develop with gusty erratic winds 25-45 kt possible Friday afternoon and evening. Local reductions in visibility from wildfire smoke. Surface winds: SW-NW 5-15 kt, gusts to 25 kt Friday afternoon. Winds aloft at 10kft MSL: SW 15-25 kt.

KBOI...VFR. Increasing mid to high clouds with light showers or virga in the vicinity overnight into Friday. Surface winds variable less than 10 kt overnight, then SE 5-15 kt developing by Friday afternoon.

Weekend Outlook...Mainly VFR. Patchy morning fog in the west central Idaho mountains and scattered showers on Saturday through the day in Idaho, mainly in the mountains. Slight chance of thunderstorms in the afternoon. SW-NW surface winds 5-15 kt with gusts to around 25 kt. Breezy W-NW winds and dry on Sunday.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.