textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Isolated afternoon showers and thunderstorms on Thursday over the higher terrain of southwest Idaho and along the Nevada border.

- Warm and dry Friday and Saturday.

- High chance of thunderstorms Sunday evening through Wednesday, with most storm activity on Monday and Tuesday evenings.

SHORT TERM /Through Saturday Night/

Issued 239 AM MDT THU APR 30 2026 The slow moving upper level trough is finally moving out of the area, but not before one final hoorah in isolated afternoon showers and thunderstorms today. The chance of precipitation is only a meager 10% over the Boise mtns and Idaho-Nevada border. However, showers and storms that form will be capable of producing outflows up to 25 mph and small hail. Otherwise, Friday and Saturday are sunny and dry as high pressure builds behind the exiting trough. Temperatures will rise to 5-10 degrees above normal, exhibited as afternoon high temperatures in the mid- upper 70s in lower elevations. Saturday will be a few degrees warmer than Friday, though a developing cut off low off the coast will bring increasing clouds.

LONG TERM /Sunday through Thursday/

Issued 239 AM MDT THU APR 30 2026 A cut off low will strengthen off the coast Sunday. By that evening, the low's moisture stream and colder temperatures aloft will edge into the southwest portion of our forecast area. Even though it is a few days out, the GFS already shows 100-200 J/kg of CAPE over the area. With precipitation chances of 20-30% in southern Oregon and southwest Idaho along the Nevada border, the environment should support development of thunderstorms as early as Sunday evening. This trend only continues Monday and Tuesday as the low moves inland, with CAPE values climbing to 400-700 J/kg in the evening both days. Storms will be capable of producing strong winds and hail. Precipitable water inside the low's airmass rises to the 80-90th percentile for this time of year, so moderate-heavy rainfall is expected in storms. While cut off lows are notoriously unpredictable, models are in broad agreement on the forecast at this point. Tuesday night through the rest of the long term, the low moves south and east, high pressure taking it's place. Thus, a return to warm and dry weather is expected.

AVIATION /12Z Thursday through Friday/

Issued 503 AM MDT THU APR 30 2026 VFR. Isolated showers and weak storms develop over the Boise Mtns and ID-NV border this afternoon. Outflow gusts up to 25 kt. Surface winds: SE-NE 5-15 kt, becoming NE-NW this afternoon. Gusts up to 20 kt possible in highlands. Winds aloft at 10kft MSL: E up to 10 kt.

KBOI...VFR. Isolated showers over Boise Mtns Thursday PM, with potential for E-NE 20-30 kt outflow wind gusts to reach KBOI late afternoon. Surface winds: SE 3-8 kt, transitioning to NE-NW around Thu/21Z.

Weekend Outlook...Saturday VFR with increasing mid-high clouds. Slight chance of thunderstorms in south-central Oregon. Winds S-SE 10-20 kt. Higher chance of thunderstorms Sunday afternoon in SE Oregon, ID-NV border, and central Idaho mtns. Winds Sunday E 5-15 kt.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.