textproduct: Boise

KEY MESSAGES

- Continued very warm and dry through Friday but becoming windier Friday afternoon.

- Much cooler, with showers, Saturday through Thursday. Snow above 6000 feet. Quite cold in Oregon Sunday morning.

- Significant rainfall possible in south-central Idaho Sunday through Tuesday.

SHORT TERM /Through Saturday Night/

An upper level ridge will continue the warm and dry weather through Friday. However, winds will increase Friday ahead of a strong cold front and supporting upper level trough that will come in from the northwest late Friday night and Saturday. Gusts to 35 mph will develop Friday afternoon in the higher elevations and in southeast Oregon and far southwest Idaho. The strong cold front will move across the area late Friday night and Saturday morning. High temps will be 20 to 30 degrees cooler on Saturday along with breezy northwest winds. The upper level trough will become a closed low and move southwestward to the California coast by Sunday where it can entrain remnants of weakening Hurricane Rachel off Baja California. Southerly winds aloft will then begin to circulate Rachel's moisture toward our CWA, especially toward south-central Idaho where heavy rainfall is becoming an increasing possibility. Meanwhile, Oregon will stay relatively dry but also colder, the coldest so far this season, with lows Sunday morning generally in the 20s.

LONG TERM /Sunday through Thursday/

Cool and unsettled conditions will continue into Sunday. As the low that will bring us our cool down digs south into the Great Basin, moisture from Rachel will be transported north in the southerly flow aloft. While the bulk of this remnant moisture should remain to our east and south, there is still some uncertainty in the westward extent of it. How far into our area it gets will influence precipitation totals generally from Mountain Home on east. Right now, the forecast carries around a half inch of precip over the western Magic Valley and Boise Mountains, tapering off as you move west to around 0.05 inches at Boise from Sunday 6am MDT to Monday 6am MDT. However, these totals will be higher should the plume of remnant moisture set up a little farther west. The latest NBM 75th percentile QPF over that period gets to around an inch in the western Magic Valley, which would be a reasonable higher end total. The potential for significant rainfall will continue to be monitored in the days to come. The southerly flow aloft will keep snow levels on the higher side across SW-Idaho this weekend, with snow levels ranging from 7-9 kft MSL. Temperatures on Sunday will drop to 5-10 degrees below normal, with localized frost/freeze conditions Sunday morning before more widespread frost/freeze conditions Monday morning. To put it simply, expect cool, cloudy, and rainy conditions Sunday into Monday across SW Idaho.

As the low moves east through Tuesday, uncertainty remains on how far north/south it will track and whether or not our area will get into the wrap-around precip associated with it. For now, we are maintaining the 20-40% chance of precipitation come Tuesday, highest in southern and central Idaho. Come Wednesday, the dynamic pattern looks to continue, with ensembles coming into agreement on a shortwave trough moving across the Northern Rockies before ridging sets in off the coast come Thursday. The shortwave trough will aid in maintaining cooler than normal temperatures through mid week, with precipitation favored over the Central Idaho Mountains. With light snow accumulations possible above 6-7 kft MSL.

AVIATION /18Z Thursday through Friday/

Issued 1141 AM MDT THU OCT 8 2026

VFR and clear, except areas of smoke/haze reducing visibility near prescribed burns, most likely to occur near KMYL. Surface winds: Variable less than 12 kt. Winds aloft at 10kft MSL: SW-NW 5-15 kt.

KBOI...VFR and clear. Surface winds: Becoming NW 4-8 kt this afternoon. SE 5-10 kt by mid-evening.

Weekend Outlook...Increasing clouds late Fri with a 5-10% chance of showers/storms late afternoon and evening. A cold front moves through Fri night with rain and snow developing across the north. 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 to 8 PM MDT Friday for IDZ423-426. OR...None.