textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Warm and mostly dry today ahead of a strong cold front late tonight 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 the middle of next week, then a warming and drying trend likely for the weekend.

SHORT TERM /Through Monday Night/

Issued 327 AM MDT SAT SEP 12 2026 Warm and dry conditions will continue for most of the day today, with valley high temperatures climbing to the mid 80s. A strong low pressure system will move into the Pacific Northwest this evening, with an associated cold front moving through the region overnight. The cold front will initially track into southeast Oregon by the late evening, bringing elevated southwest winds with gusts up to 45 mph and scattered showers over Baker County and northern portions of Malheur/Harney County. The front will then progress into southwest Idaho overnight, bringing wind gusts around 35 mph (ridgetop gusts up to 45 mph) and scattered showers northeast of the Snake River Valley. Instability remains weak with surface CAPE values less than 100-150 J/kg, especially given the timing of the frontal passage, but a 10-20% chance of thunderstorms will accompany showers. The best chance for thunderstorms will be over Baker County, OR into Valley County, ID during late evening. Models continue to track the bulk of the moisture and the low center north and west of the region, which further decreases potential for precipitation accumulation. Current forecasts only show 0.25-0.50 inches of precipitation by Sunday morning, a significant reduction compared to previous forecasts. Temperatures will drop for Sunday by about 15-20 degrees, with snow levels dropping down to 6,500-7,500 feet MSL. Minimal snow will fall over higher terrain, with accumulations of less than an inch primarily over the Wallowa/Seven Devils Mountain Ranges. Troughing will continue through Monday, with cool conditions lingering. Patchy valley fog will form in mountain valleys on Sunday and Monday morning.

LONG TERM /Tuesday through Saturday/

Issued 327 AM MDT SAT SEP 12 2026 A long wave trough will deepen into the Intermountain West through Wednesday, bringing cool temperatures and a low chance of showers on Wednesday into Thursday. The trough will then move east as a ridge of high pressure will develop over the western US by the latter half of the week. Some model disagreement delays the trough's exit out of the region, which would keep cool and wet conditions lingering through the end of the work week. However, the bulk of model solutions keep the ridge of high pressure for the weekend, bringing above normal temperatures and dry conditions likely for Friday into Saturday.

AVIATION /12Z Saturday through Sunday/

Issued 601 AM MDT SAT SEP 12 2026

VFR through this evening. Cold front arrives late with increasing showers across eastern Oregon and w-central ID. A 10% chance of lightning. Localized MVFR and mountain obscuration in showers. Surface winds: SE-SW 5-15 kt, with gusts to 25-30 kt this evening in eastern Oregon and Owyhee Mountains. Winds aloft at 10kft MSL: W-SW 20-35 kt.

KBOI...VFR. Surface winds: SE 5-12 kt. Shifting to gusty SW-NW 10-15 kt with gusts to 25 kt tonight with cold front.

Sunday Outlook...Generally VFR. Showers and 10% chance of lightning across E Oregon and w-central Idaho. Localized MVFR and mountain obscuration in showers. Patchy mountain valley fog, mixing out by late 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 today to 9 PM MDT this evening for IDZ423-426. OR...None.