textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Rain and high elevation snow across southeast Oregon today, with thunderstorms this afternoon and evening across the southwest Idaho mountains.

- Much cooler today with gusts 30-45 mph developing by this evening.

- Additional showers and thunderstorms and periods of gusty winds Wednesday through Sunday.

- Thunderstorms may produce gusty winds 40-60 mph and blowing dust, brief heavy rain, and hail this week.

SHORT TERM /Through Thursday Night/

Issued 308 AM MDT TUE MAY 26 2026 An upper low will bring active weather to the area through much of the short term. The low, located over southwest Oregon this morning, will slowly shift south and then stall over northern California and western Nevada through mid week. It will be much cooler today in eastern Oregon today (20-30 degrees cooler) due to the proximity of the low, but cooling will be less pronounced in southwest Idaho (10-20 degrees cooler). Rain and high elevation snow above 5500-7000 feet will increase this morning across Harney County Oregon closer to the low center, then expand across southeast Oregon and far southwest Idaho this afternoon.

Meanwhile, instability will increase this afternoon and evening in the warm sector across the southwest Idaho mountains. A surface low and shortwave trough rotating around the upper low will aid lift for shower and thunderstorm development. Storms will move north-northwest this evening and are favored to remain over the mountains, with about a 20% chance of a thunderstorm drifting west over the Treasure Valley. Thunderstorms may produce brief heavy rain, small hail, and gusty outflow winds 40-60 mph which may produce blowing dust. Showers will also expand in coverage this evening outside of thunderstorms. Precipitation amounts of 0.25-0.50" through tonight are expected in Harney County, locally up to 1", with lower amounts elsewhere. Rainfall amounts from thunderstorms will be highly variable, but up to 1" will be possible from the strongest storms. Outside of thunderstorms, expect gusty northwest winds, strongest this evening with gusts 30-45 mph owing to a tight pressure gradient across the area.

As the low stalls Wednesday and Thursday, south to southeasterly flow across the area will bring around 10 degrees of warming from Tuesday, with the coolest temperatures persisting along the Oregon/Nevada border. Moisture will continue to rotate around the low, bringing periodic chances of showers and thunderstorms. The highest chance will be across southeast Oregon, as well as each afternoon and evening across the mountains of southwest Idaho as daytime heating increases instability. Warmer surface temperatures will support more instability than today, and there will be enough shear for localized stronger thunderstorms capable of producing gusty outflow winds and hail. Outside of storms, expect gusty southeast winds, strongest across southern areas each afternoon with gusts 20-40 mph.

LONG TERM /Friday through Tuesday/

Issued 308 AM MDT TUE MAY 26 2026 Active weather will continue to end the week. A trough digging down the coast of British Columbia will steer the filling low, that's been stagnant over the Great Basin, northward over our area. As this low lifts, showers will continue to make themselves known through Friday and Saturday. Ensembles continue to resolve sufficient instability building in, with surface heading and height falls aloft, to support a threat of thunderstorms come Friday afternoon. Come Saturday, the greatest precipitation chances (50-85%, increasing as you move northeast) will be over the West Central Mountains. While instability will be weak, mountain thunderstorms Saturday afternoon can't be ruled out. The shortwave will also give way to breezy conditions to end the week.

Guidance hints at a weak shortwave, associated with the aforementioned trough, crossing over our area Sunday. However, a dry slot will limit moisture availability, limiting slight precipitation chances to higher terrain. Temperatures through the weekend will generally be at or leaning below normal. As the shortwave exits our area late Sunday/early Monday, a building ridge will support a warming trend to start next week. By Tuesday, temperatures will be up to around 10 degrees above normal.

AVIATION /12Z Tuesday through Wednesday/

Issued 518 AM MDT TUE MAY 26 2026

Generally VFR. Scattered showers continuing throughout the day, expanding in coverage this afternoon. Thunderstorms developing across central ID this afternoon, capable of small hail, and outflows to 20-40 kt. Ceilings lowering to MVFR near KBKE/KBNO this afternoon. Precip tapering off early Wed/AM. Surface winds outside of storms: SW-NW 5-15 kt this morning, increasing to 10-20 kt with gusts to 20-35 kt this afternoon. Winds aloft at 10kft MSL: S-SW 10-30 kt.

KBOI...VFR. Occasional weak showers/virga this morning, with erratic outflows possible. Scattered showers this afternoon with a 20% chance of lightning. Surface winds: NW 8-12 kt this morning, then NW 15-20 kt with gusts to 25-30 kt this afternoon.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.