textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Warm and mostly dry today and tomorrow ahead of a strong cold front late tomorrow night with scattered showers, isolated thunderstorms, high elevation snow, and gusty westerly winds.

- Breezy and much cooler Sunday, with lingering showers in northeast OR and the central ID mountains.

- Unsettled cool conditions through next Wednesday, then a warming and drying trend likely for the end of the week.

SHORT TERM /Through Sunday Night/

Issued 209 PM MDT FRI SEP 11 2026 Warm and dry tonight under a weak trough. A strong Pacific upper low is currently tracking toward the Northwest coast and is expected to reach the coast Saturday afternoon. Recent model guidance has continued the trend of a slower low progression as well as nudged the core of the upper level low further north as it tracks inland overnight Saturday into Sunday. Ahead of this system on Saturday, strong southwesterly flow aloft will tap into warm air and push high temperatures back up near 5 to 8 degrees above seasonal averages. However, the slower timing will delay the precipitation to late Saturday evening. Pre-frontal pressure gradients will produce gusty southwesterly surface winds, gusting 35 to 45 mph across southeast Oregon and the Snake River Plain down to the Nevada border. In addition to the warmth, southwesterly upper level wind looks to transport a layer of wildfire smoke northeastward from fires in California, leading to increasing haziness across southeast Oregon and southwest Idaho through Saturday afternoon.

The primary cold front will push west-to-east across the area late Saturday evening with showers and thunderstorms possible north of a Rome-Ontario-Stanley line into Sunday morning. Instability is marginal at best but enough to warrant a slight chance for thunderstorms overnight. The best chance for showers and thunderstorms will be largely focused across Baker County in Oregon and central Idaho north of the Snake River Basin.

The cold front crosses southwest Idaho Sunday morning continuing the windy conditions across much of the area into Sunday afternoon. Temperatures will plummet roughly 15 to 20 degrees below Saturday highs. Showers linger across the northern and eastern mountain zones Sunday morning before tapering off Sunday afternoon. Snow levels will drop to 7000 to 8000 feet MSL, bringing light snow accumulations to the high mountain peaks. Clearing skies Sunday night and lighter winds will support rapid radiational cooling, leading to a cold night area-wide and potential patchy valley fog early Monday morning.

LONG TERM /Monday through Friday/

Issued 209 PM MDT FRI SEP 11 2026 As the low pressure system from the weekend moves eastward, troughing continues along the west coast. The troughing will bring southwesterly flow and eventually strengthen into a closed low that rejoins the broader flow later in the week. The period from Monday through Wednesday will see steadily warming temperatures as the trough and low build. There is a very low chance of showers over high terrain during this time frame as the closed low blocks the bulk of Pacific moisture from reaching the area. Models have shown little run to run consistency on the track of the closed low as it becomes a longwave trough later in the week. A high amplitude ridge follows closely behind, threatening to continue warming conditions with drier weather if the trough misses us. However, the latest runs of long range models show the trough bringing us higher chances for precipitation Thursday and Friday.

AVIATION /06Z Saturday through Sunday/

Issued 1138 PM MDT FRI SEP 11 2026

VFR through Saturday. Cold front arrives this evening with increasing showers across E Oregon and w-central ID. A 10% chance of lightning. Localized MVFR and mountain obscuration in showers. Surface winds: variable up to 10 kt. Then, SE-SW 5-15 kt this afternoon, with gusts to 25-30 kt in E Oregon and Owyhee Mountains. Winds aloft at 10kft MSL: W-SW 15-30 kt.

KBOI...VFR. Surface winds: SE 5-12 kt. Shifting to gusty SW-NW tonight with cold front.

Sunday Outlook...Generally VFR. Showers and 10% chance of lightning across E Oregon and w-central Idaho Sunday morning, and again Sunday afternoon. Localized MVFR and mountain obscuration in showers. Patchy mountain valley fog Sunday morning. Snow levels 6500-7500 ft MSL by Sunday morning. Surface winds Sunday: SW-NW 5-15 kt, with PM gusts around 20-25 kt.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Red Flag Warning from noon to 9 PM MDT Saturday for IDZ423-426. OR...None.