textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Slight warming and drying trend Tuesday and Wednesday, with light winds.

- Cold temperatures tonight will bring patchy fog and frost to the mountain valleys.

- A low pressure system will bring light precipitation and isolated afternoon thunderstorms across the area Thursday and Friday.

SHORT TERM /Through Thursday Night/

Issued 318 AM MDT TUE SEP 15 2026 Overnight lows in high terrain will approach freezing, bringing patchy valley fog and frost this morning. Southwest flow aloft will keep daytime temperatures warm and conditions mostly dry today and tomorrow. Winds will generally be light and terrain driven, with mostly sunny skies. On Wednesday, a low pressure system over western Oregon will deepen and move slightly further east compared to previous model runs. This will bring a 40-60% chance of precipitation over the region on Thursday, with a slight chance of afternoon thunderstorms over northern zones. Two day rainfall accumulations will total between 0.05-0.15 inches, with higher elevations in the West Central Mountains approaching 0.50-0.75 inches of rain. Warm daytime temperatures will keep snow levels above 9,000-10,000 feet MSL through the short and long term period. Southerly winds will be elevated over south central Idaho as the low moves into the region on Thursday, with gusts up to 35 mph.

LONG TERM /Friday through Tuesday/

Issued 318 AM MDT TUE SEP 15 2026 Precipitation chances look to decrease across the region on Friday, but mountains in central Idaho and northeast Oregon look to keep at least a 30-40% chance of showers and a 10-15% chance of thunderstorms through Friday night. Southerly flow aloft will keep temperatures near normal through Friday, ahead of cooler temperatures on Saturday with the low center moving over the region. The low pressure system will then exit to the east on Saturday, with showers and cooler temperatures lingering over the central Idaho mountains. High pressure will build in over the region on Sunday, with temperatures trending slightly above normal (3-5 degrees) on Monday. A cold front associated with a broad upper level trough then looks to move in sometime on Tuesday, bringing slightly cooler temperatures and a slight chance of mountain rain showers.

AVIATION /12Z Tuesday through Wednesday/

Issued 605 AM MDT TUE SEP 15 2026

Generally VFR. Increasing high clouds this afternoon, mainly north and west of KTWF/KJER. Surface winds: variable under 10 kt becoming E-SE 5-10 kt after Tues/17Z. Winds aloft at 10kft MSL: W-SW 10-20 kt.

KBOI...VFR. Increasing high clouds this afternoon. Surface winds: SE 4-10 kt then W-NW 3-5 kt by early afternoon.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.