textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Virga and light rain today through early Monday, with highest rain chances across east Oregon and the west-central Idaho mountains.

- Warm and dry conditions expected Tuesday through next weekend, with max temperatures peaking Wednesday and Thursday.

SHORT TERM /Through Tuesday Night/

Issued 230 AM MDT SUN SEP 27 2026 Southeast Oregon and southwest Idaho reside under southwest flow aloft this morning ahead of a weak trough over the West Coast. This trough is spreading a swath of mid-level moisture across the area today through early Monday, bringing cloudy skies, widespread virga, and light rain. While precipitation is expected to be sporadic as moisture expands northward, the highest probabilities of measurable rainfall are over east Oregon and west-central Idaho (20-40%) mainly in the afternoon and evening...with lower chances (5-15%) elsewhere. Southwest to northwest surface winds will become breezy this afternoon across southeast Oregon and portions of the western Snake Plain. As the trough heads eastward overnight into early Monday, the moisture will also depart toward the east. As a result, skies will begin to clear and temperatures will trend warmer for Monday compared to previous days. Westerly flow aloft will establish over the region beginning Tuesday, with dry and warm conditions anticipated.

LONG TERM /Wednesday through Sunday/

Issued 230 AM MDT SUN SEP 27 2026 Forecast models depict a building ridge over the southwestern U.S. from Tuesday through Thursday, driving lower-elevation temperatures into the upper 70s/low 80s by Wed and Thu. Thereafter, a weak shortwave trough will enter the Pacific Northwest on Friday, briefly flattening the ridge and dropping temperatures by a few degrees Friday through Saturday. Moisture associated with this trough is likely to remain north, keeping southeast Oregon and southwest Idaho in a drier airmass. The ridge is expected to rebound on Sunday as the trough continues east, supporting the return of above normal temperatures.

AVIATION /12Z Sunday through Monday/

Issued 529 AM MDT SUN SEP 27 2026

Generally VFR. Virga and isolated/scattered light rain showers will expand north across the area today. Surface winds: variable less than 10 kt through morning. Becoming SW-NW 5-15 kt, with gusts to 25 kt south/east of KBOI after Sun/21Z. Winds aloft at 10kft MSL: SW 10-20 kt.

KBOI...VFR. Virga or light rain in the vicinity through morning. A 15% chance of rain reaching the ground at the terminal. Surface winds: light SE or variable through morning, becoming NW 7-14 kt this afternoon, with gusts to around 20 kt mid- afternoon through early evening.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.