textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Isolated showers and thunderstorms today. Stronger storms producing gusty winds possible in SW Idaho.

- Cool and dry Sunday then warmer early next week.

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

SHORT TERM /Through Monday Night/

Issued 242 AM MDT SAT AUG 29 2026 Upper level low over the Pacific Northwest today will keep mid level moisture across the forecast area. Sub-cloud moisture combined with steep low level lapse rates this afternoon should foster convective development. While widespread severe weather is not anticipated, isolated strong thunderstorms over southwest Idaho, mainly south of a Rome-Ontario-Stanley line, could produce localized outflow wind gusts up to 55 mph along with brief heavy rain. Convective activity will taper off across eastern Oregon late this afternoon, while shower and thunderstorm chances persist across central and southern Idaho into the evening hours.

A broader upper level trough and cold front will advance from the Pacific Northwest late Saturday into Sunday morning. Latest high-res model guidance has significantly lowered the convective threat ahead of the front across the West-Central Mountains Saturday evening to the point where most have removed showers and thunderstorms altogether. The cold frontal passage late Saturday evening into Sunday morning will usher in cooler, drier air along with gusty northwest winds across the region. High temperatures on Sunday will drop 5 to 10 degrees below seasonal averages with patchy frost possible Sunday and Monday morning across the higher valleys of southeast Oregon.

Brief shortwave ridging on Monday will allow temperatures to rebound back toward normal levels, though shower chances will begin to return to south central Idaho late Monday night with the approach of the next upper level low pressure system.

LONG TERM /Tuesday through Saturday/

Issued 242 AM MDT SAT AUG 29 2026 The long term period will feature an active and persistent trough pattern across the western United States. An amplifying trough off the Pacific Northwest coast will push another shortwave disturbance inland on Tuesday, bringing increased chances for showers and thunderstorms, mainly across the higher terrain.

A stronger closed low will dig along the trough axis Wednesday through Friday, stalling near the Pacific Northwest coast. This positioning will keep southeast Oregon and southwest Idaho under cool, unsettled southwesterly flow aloft. High temperatures will fall roughly 10 degrees below normal for early September, with valley highs remaining in the 70s. Tightening surface pressure gradients and strong mid level winds mixing down each afternoon will generate widespread breezy to windy conditions Tuesday through Saturday. Shower and thunderstorm timing will remain tied to minor individual shortwaves rotating around the parent trough.

AVIATION /12Z Saturday through Sunday/

Issued 602 AM MDT SAT AUG 29 2026 Mid to high clouds today. Isolated thunderstorms with gusty erratic winds 25-45 kt possible this afternoon mainly across south-central Idaho. Local reductions in visibility from wildfire smoke. Surface winds: SE-W 5-15 kt, becoming NW Saturday evening along a cold front. Localized gusts 15-25 kt overnight, with gusts 20-30 kt Saturday afternoon/evening. Winds aloft at 10kft MSL: SW 15- 25 kt.

KBOI...Overcast mid to high clouds. A 10% chance of a thunderstorm late afternoon/evening. Surface winds NW 5-15 kt today. Winds increasing this afternoon with gusts up to 25 kt.

Sunday Outlook...Decreasing clouds and dry. Surface winds W-NW 5-15 kt, afternoon gusts 20-25 kt in S-central Idaho.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.