textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Areas of valley fog early this morning.

- Warmer and drier today but still cooler than normal.

- Widespread showers and slight chance of thunderstorms late Sunday through Monday.

- Cooler Monday, then warming next week, with a slight chance of thunderstorms Wednesday afternoon through Friday.

SHORT TERM /Through Monday Night/

Issued 210 AM MDT SAT SEP 5 2026 At 1 AM MDT satellite and radar showed a band of showers and isolated thunderstorms extending from nw Montana ssw-ward through western ID to north-central NV. The band was shifting slowly east and should be out of CWA by sunrise. Radar also showed a couple of thunderstorms in central OR closer to a deep upper low still centered along the OR coast. The low will stay there through Sunday, then move inland across OR Sunday night, western ID Monday morning, then northeastward into MT Monday afternoon. This track is slightly south of yesterday's forecast track, and places the low more directly over our CWA late Sunday night and Monday morning. As a result, our CWA should have slightly more pcpn than previously forecast, especially our northern zones, along with slightly lower temps, and lower snow levels. We still have a slight (20%) chance of thunderstorms throughout our CWA Sunday evening, then retreating to the central ID mountains Sunday night and Monday morning. Back to today: Today looks sunnier, warmer, and drier than Friday, especially in Idaho where highs Friday were only in the 50s to lower 60s. Today's highs will be generally in the 70s, with 60s in the mountains. Instability will allow a 20% chance of showers and thunderstorms late today, but only in eastern Valley County/ID and western Baker County/OR. Latest models develop another NNE-SSW band of showers again late tonight through early Sunday morning in western ID. The incoming upper low will begin more general showers and thunderstorms in eastern OR Sunday, followed by widespread rain and high-mountain snow Sunday night and Monday morning, decreasing Monday afternoon, and ending Monday night. The wet weather will be followed by areas of valley fog after midnight. Total pcpn Sunday through Monday should be near 1.00 inch in eastern Valley County/ID, .25 to .50 inch in other northern zones and southern mountains, and generally .10 to .25 inch in southern zones. The larger amounts again create concern for flash flooding on the Wapiti Burn scar (to be addressed in more detail later today). Monday should also be 6 to 12 degrees cooler than Sunday.

LONG TERM /Tuesday through Saturday/

Issued 210 AM MDT SAT SEP 5 2026 Latest models show the upper low exiting our CWA Monday before tropical moisture can get into the low's circulation, which means our CWA should miss out on that moisture. But a weak upper trough from the north Pacific will still produce a slight chance of late-day showers Wednesday and Thursday. Temperatures on those days will be slightly above normal, with Friday likely even a little warmer. A cold front and stronger upper trough should bring windy, cooler weather Friday night and Saturday, with a better chance of showers.

AVIATION /18Z Saturday through Sunday/

Issued 1155 AM MDT SAT SEP 5 2026 Valley fog/stratus mostly cleared up by now. Isolated showers and thunderstorms this afternoon in eastern Oregon and the central ID mountains. Surface winds: becoming NW 5-15 kt this afternoon. Winds aloft at 10kft MSL: S 10-20 kt.

KBOI...VFR with a low chance of showers after midnight tonight. Winds mostly light and variable, but generally out of the NW this afternoon.

Sunday Outlook...Scattered showers and thunderstorm spreading eastward across OR, reaching western ID late afternoon. Patchy valley low stratus/fog Sunday morning. SW-NW surface winds 5-15 kt with PM gusts to 20kt.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.