textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Scattered thunderstorms this afternoon into early Saturday could produce strong outflow winds, small hail and brief heavy rain.

- Temperatures around 15 to 20 degrees below normal Saturday and Sunday.

- Significant precipitation and light snow above 7000 feet possible Saturday through Sunday.

SHORT TERM /Through Sunday Night/

Issued 213 PM MDT FRI JUN 26 2026 The main focus through late this evening will be the potential for strong thunderstorms developing across the region. Clearing of skies across southeast Oregon has allowed for surface heating for modest instability (SBCAPE of 50 to 200 J/kg) and the initiation of thunderstorms across southeast Oregon. Initial convective activity will be capable of producing strong, erratic outflow wind gusts up to 50 mph due to relatively dry low- levels. However, as atmospheric moisture steadily increases overnight, this severe wind threat will gradually diminish and storms will produce brief heavy rain and small hail.

Thunderstorm activity is expected to persist through the overnight hours and continue through Saturday across much of the forecast area. With the added moisture, storms will become capable of producing heavy rainfall and small hail. The best dynamics, moisture pooling, and overall chance for storms and heavier rainfall amounts will focus across southwest Idaho. The potential for heavier rainfall across the central Idaho mountains Saturday increases the potential for rock slides and localized flooding especially near legacy burn scars, like the Wapiti fire burn scar and will need to be monitored.

Convective activity and overall precipitation chances will begin to taper off early Sunday as the system starts to exit the region. Showers and thunderstorms will persist on the backside of the low across the central Idaho mountains as well as Baker County and along the Idaho/Nevada border.

Precipitation amounts of 1 to 1.25 inches are possible over the central Idaho mountains through Sunday. Lesser amounts are expected in eastern Oregon, where 0.25 to 0.75 inches is forecast, while the Snake River Plain will generally see between 0.25 and 0.50 inches. Above 6500 feet could see up to 3 inches of wet snow Saturday night into Sunday. Temperatures will plummet to around 20 degrees below normal Saturday and Sunday. Several locations are forecast to approach record low maximum temperatures for the day both days. Near record low temperatures are also possible across southeast Oregon Sunday morning.

LONG TERM /Monday through Friday/

Issued 213 PM MDT FRI JUN 26 2026 Gradual warming and drying Monday and Tuesday as the weekend upper low moves away into central Canada, but leaves behind weak residual troughing for a continuing chance of showers and thunderstorms in northern mountains. On Wednesday another cold upper level low will approach from the BC coast. This second low is not as cold as the current low and models are not yet in agreement about where it will go, so forecast confidence beyond Wednesday is low. For now we're going with the warmer ECMWF forecast which takes the low inland across BC and Alberta, and keeps our CWA generally dry with temperatures close to normal. We also have a slight chance of showers and thunderstorms over northern mountains Thursday and Friday. The GFS, on the other hand, would bring the low all the way south to the southern Panhandle, with greater chances of showers and thunderstorms, and temperatures well below normal again.

AVIATION /00Z Saturday through Sunday/

Issued 555 PM MDT FRI JUN 26 2026

Generally VFR. Scattered/numerous showers and thunderstorms bringing localized MVFR, erratic gusts to 25-35 kt, small hail, and brief heavy rain. Lightning coverage will decrease overnight, but increase again Sat morning. Mtns obscured. Surface winds outside of storms: variable 5-15 kt, then W-NW 5-15 kt with gusts to 20-25 kt after Sat/16Z. Winds aloft at 10kft MSL: W-SW 15-25 kt.

KBOI...Generally VFR. Periods of rain showers continuing through Saturday evening. Threat of thunderstorms this evening prior to Sat/05Z, and again Sat afternoon. Thunderstorms capable of gusts to 25-35 kt, brief heavy rain with lowered vis, and small hail. Surface winds: variable 5-15 kt this evening, especially around shower activity. Then, W-NW 5-15 kt overnight and Sat.

Weekend Outlook...Numerous showers through Sunday. Lightning activity will taper off for Sat night/Sunday. Mtn obscuration. Local MVFR/IFR over mountains in rain/snow. Snow level lowering to 6500-7500ft MSL Sunday morning. Gusty west-northwest surface winds Sunday afternoon.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Red Flag Warning until 6 AM MDT Saturday for IDZ400-420-423- 424-426. OR...Red Flag Warning until 6 AM MDT /5 AM PDT/ Saturday for ORZ670>674.