textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- A significant pattern change arrives Friday as a cool upper level trough pushes a cold front through, bringing widespread showers, scattered thunderstorms and cooler temperatures.

- Scattered thunderstorms Friday 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 Saturday Night/

Issued 218 PM MDT THU JUN 25 2026 An upper level low and cold front moving into the region early Friday morning will begin a significant pattern shift. The cold front will cross the area Friday morning, bringing light showers and gusty winds. Partial clearing behind the front in the afternoon will allow for the development of scattered thunderstorms. Storms are expected to initiate across southeast Oregon around noontime, then track eastward into southwest Idaho late Friday afternoon and early evening.

Despite increasing moisture aloft, low levels will remain quite dry through at least early Friday evening, increasing the risk for strong, erratic outflow winds from any storms. The lower levels will eventually moisten up overnight, with storms transitioning to a threat for brief heavy rain and small hail. This heavy rain threat will be most pronounced by Saturday morning as the bulk of the convective activity shifts into southwest Idaho. The upper level trough will provide ample dynamic support to keep thunderstorms going overnight Friday into Saturday.

As the center of the low moves into the region on Saturday, shower and thunderstorm activity will focus heavily across southwest Idaho. Precipitable water (PW) values are progged to peak around the 90th percentile Saturday morning, supporting storms capable of producing brief heavy rain through Saturday evening. Precipitation amounts of up to 1 to 1.25 inches are possible over the central Idaho mountains. Lesser amounts are expected in eastern Oregon, where 0.25 to 0.50 inches is forecast, while the Snake River Plain will generally see between 0.25 and 0.50 inches.Temperatures will plummet to around 20 degrees below normal on Saturday. Several locations are forecast to approach record low maximum temperatures for the day. Precipitation and thunderstorm activity will gradually taper off from west to east late Saturday night as the core of the trough moves into the Great Basin.

LONG TERM /Sunday through Thursday/

Issued 218 PM MDT THU JUN 25 2026 A low pressure system over the Northern Rockies will continue to bring cool and showery conditions to the forecast area on Sunday, especially for west-central/central Idaho. Snow levels will temporarily lower to 6500-7500 ft MSL Sun morning, allowing light snow to fall across the high terrain. Gusty winds will develop in the afternoon, while temperatures remain 15-20 degrees below normal. A slight chance of thunderstorms is also forecast for Sunday afternoon, once again favoring central Idaho. Conditions will trend a little warmer on Monday as the low gradually departs toward the northeastward. However, unsettled conditions will linger across the Northwest through Wednesday as a secondary low approaches from BC Canada. This will keep temperatures below normal through at least Wednesday.

AVIATION /06Z Friday through Saturday/

Issued 1120 PM MDT THU JUN 25 2026 VFR. Increasing clouds. Virga and showers tonight, increasing in coverage through Fri/AM. Widely scatters showers/thunderstorms Fri/PM. Storms capable of outflows to 30-45 kt, small hail, and brief heavy rain. MVFR/IFR possible in rain/thunder, esp over mtns. Mtns obscured in precip. Surface winds outside of storms: NW 10-20 kt with gusts to 20-35 kt following frontal passage and in virga/showers. Then variable 5-15 kt Fri/PM. Winds aloft at 10kft MSL: Variable 5-20 kt.

KBOI...VFR. Virga and vicinity showers tonight, then frequent rain showers begin around Fri/13z. Increasing thunder chances (30%) Fri/PM. Thunder capable of outflows to 30-45 kt, small hail, and brief heavy rain. Surface winds outside of storms: NW-N 10-20 kt, gusts to 25-30 kt with virga/showers/cold front overnight through Fri morning. Then variable under 8 kt Fri/PM.

Weekend Outlook...Showers and thunderstorms Saturday and Sunday. Brief MVFR/IFR possible in heavy rain or snow, esp over mtns. Mountains obscured. Snow levels temporarily lowering to 6500-7500ft MSL Sunday morning. Gusty west-northwest surface winds during the afternoons.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Red Flag Warning from noon Friday to 6 AM MDT Saturday for IDZ400-420-423-424-426. OR...Red Flag Warning from noon MDT /11 AM PDT/ Friday to 6 AM MDT /5 AM PDT/ Saturday for ORZ670>674.