textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Continued very warm and dry conditions through Friday but becoming windy in the afternoon.

- Active pattern bringing cooler conditions and precipitation chances Saturday through Wednesday. Snow showers above 6000 feet this weekend.

- Significant rainfall possible in south-central/west-central Idaho late Saturday through Tuesday.

SHORT TERM /Through Sunday Night/

Issued 349 AM MDT FRI OCT 9 2026 Today will be the last day of warm temperatures 10 to 20 degrees above normal, as the persistent upper ridge gradually breaks down ahead of an approaching Pacific upper trough from British Columbia. Ahead of an approaching cold front associated with this low passage, winds will increase considerably in the afternoon today, with gusts up to 35 kt over higher terrain areas. Very dry conditions, with minimum relative humidities in the lower teens, will still be expected today, especially over the southern half of our CWA. The cold front will pass over our area late tonight through early Saturday, bringing a 20-30% chance of rain showers over southwest ID and east-central OR. The frontal passage will bring a sharp cooldown with peak temperatures dropping 20 to 30 degrees on Saturday.

Saturday through Sunday, the upper low center will begin diving down into the northwest region and capture a massive moisture plume from the remnants of Tropical Storm Rachel off Baja California. The moisture plume will arrive just east of our area over eastern/central ID by late Saturday, bringing increased heavy rainfall chances over west-central and south-central ID. Eastern OR will stay on the relatively drier side Saturday, as the drier low center slowly moves into the area. Cool and unsettled conditions will continue into Sunday, but there is considerable uncertainty with the track of the upper low as it digs further down into the northwest region. For now, the overall guidance generally has the bulk of the moisture plume staying on the ID side, increasing precipitation chances to 40-70% over much of western ID and far southeast OR on Sunday. Projected precipitation totals for the weekend are now sitting around half an inch over the western Magic Valley and central ID mountains, tapering off west to around 0.05 inches over the Treasure Valley ID areas and far southeast OR. With snow levels expected to lower into the 4000-6000 ft MSL range on the eastern OR side and into the 6000-8500 ft MSL range on the western ID side by Sunday, snow showers and wintry mixes are likely over higher terrain areas late Saturday into Sunday, with accumulations limited to high mountain peaks.

LONG TERM /Monday through Friday/

Issued 349 AM MDT FRI OCT 9 2026 Come Monday, there remains considerable guidance uncertainty over the final track of the closed upper low as it either shifts slightly eastward directly over our area into the upper Great Basin or immediately dig further down into southern California. For now, the bulk of the advected moisture from the projected remnant of Tropical Storm Rachel will steer further northeast over the Upper Rockies by late Monday. This moisture track will keep moderate to high precipitation chances (30 to 60%) mainly over the ID side as it gradually tapers off east on Monday, with the highest chances over high terrain areas. Monday will continue seeing temperatures 5 to 10 degrees below normal with the low passage. The low passage will keep snow levels in the 4000-5000 ft MSL range on the eastern OR side, and southerly flow ahead of the approaching low will keep snow levels at 7500-9000 ft MSL on the southwest/west-central ID side, keeping the bulk of the precipitation as rain, with some light snow/wintry mix over high mountain peaks. This pattern is subject to a slight change, as the final track of the upper low remains uncertain.

As this system pushes out east, Tuesday will see around a 20-40% chance of precipitation over central and south-central ID. Come Wednesday, there is general guidance agreement over a shortwave trough digging north of us from British Columbia, possibly bringing some precip over the northernmost mountain areas of our CWA late Wednesday through early Thursday. Otherwise, a highly amplified Pacific ridge will build in and return dry conditions and a slight warming trend Thursday through Friday. Overall, near-normal seasonal temperatures will be expected throughout the long-term period.

AVIATION /18Z Friday through Saturday/

Issued 1113 AM MDT FRI OCT 9 2026

Generally VFR with increasing clouds this evening, smoke from prescribed burns resulting in localized visibility reductions, mainly near KMYL. Isolated showers developing this afternoon and continuing through Sat/AM. Surface winds: SW-NW 5-15 kt with gusts up to 25 kt in E-Oregon and higher terrain this afternoon. Becoming W-NW 10-20 kt with gusts up to 30 kt behind a cold front this evening/overnight. Gusts tapering off Sat/AM. Winds aloft at 10 kft MSL: SW 15-35 kt.

KBOI...VFR with increasing high clouds this evening. Isolated showers developing this afternoon, although a low chance of rain at terminal (<10% chance). Surface winds: NW 7-12 kt this afternoon, gusting to around 20 kt overnight following a cold front.

Weekend Outlook...Precip increases Sat, mainly across central and S-central Idaho, but may expand further west on Sun. Snow levels 6-8kft MSL across SW Idaho, 4-6kft SE Oregon. Mountains obscured at times with MVFR/IFR conditions possible in precip. Surface winds: SW-NW 10-20 kt with gusts to 30 kt across higher terrain on Fri; NW 5-15 kt with gusts 20-30 kt Sat/Sun.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Red Flag Warning from 2 PM this afternoon to 8 PM MDT this evening for IDZ423-426. OR...None.