textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Warm and dry Friday and Saturday.

- Chance of showers and thunderstorms return Sunday through Tuesday over the higher terrain of southwest Idaho and along the Nevada border.

- Heat builds Wednesday and Thursday under a drier pattern.

SHORT TERM /Through Sunday Night/

Issued 401 AM MDT FRI MAY 1 2026 After a few thunderstorms yesterday evening, an upper ridge will bring dry and stable conditions to the region, resulting in a quieter couple of days. Temperatures will warm 4 to 8 degrees each day, putting valleys into the lower 80s on Saturday as mtn valleys reach for 70. Saturday will see increasing clouds as a closed low digs along the coast. Shower and thunderstorm development on the east side of the low Saturday afternoon could spill into Harney County by evening, the potential covered by 15% chance south/west of Burns-Frenchglen-Fields. Early guidance suggests gusty outflow winds to 40 mph would accompany the showers/storms. As the low lingers off the coast on Sunday, southerly flow will increase mid-level moisture over the region. This will result in greater coverage of shower and thunderstorm development Sunday afternoon/evening. Activity will initiate over higher terrain with steering flow aloft taking activity from S to N/NW. Gusty winds will be the more widespread threat from development. Temperatures will hold steady or warm slightly from Saturday to Sunday.

LONG TERM /Monday through Friday/

Issued 401 AM MDT FRI MAY 1 2026 The upper-level cutoff low that had been sitting along the California coast will continue to move inland into the Great Basin and rejoin the flow aloft. This feature will continue to move east over the Great Basin and fully move out by late Tuesday/early Wednesday. Afternoon/evening showers and thunderstorms are the primary concerns as this system grazes by. Monday will see the highest potential for showers and thunderstorms across the area, with moisture and instability at their peak for this event. The highest precipitation chances will exist along the Nevada border for both OR and ID (20-60%), decreasing as you move north. Virtually all of the parameters used to determine thunderstorm potential (moisture, shear, instability, lift) will be largely influenced by the proximity of the low to the area, which is not entirely agreed upon by long range models. Regardless, isolated thunderstorms are forecast. Shower/thunderstorm chances will begin to trend lower on Tuesday, even more confined to the Nevada border. Precipitable water values above the 60th percentile will support heavy rain in thunderstorms, with gusty winds (accentuated by pronounced inverted- V soundings) and hail also possible.

Quickly behind this troughing feature, the upper-level ridge that has largely been sitting offshore will further build into the Pacific NW, providing the dominant pattern Tuesday through early Friday. Despite the close proximity of this upper-level trough passage to our south, temperatures through the period will be well above normal (10-15 degrees above through the week), owed to weak cold air advection. Temperatures will hover in the low-to-mid 80s in the lower elevation valleys.

AVIATION /12Z Friday through Saturday/

Issued 521 AM MDT FRI MAY 1 2026

VFR, clear skies. Surface winds: variable up to 10 kt, then E-S 5-15 kt after Fri/15Z. Winds aloft at 10kft MSL: SE-S 5-15 kt.

KBOI...VFR and clear. Surface winds: SE 5-12 kt.

Weekend Outlook...Generally VFR. Increasing mid-high clouds on Saturday with 20% chance of showers and thunderstorms in SE Oregon. Then, a 20-40% chance of showers/thunderstorms Sunday afternoon in SE Oregon, ID-NV border, and central Idaho mtns. Surface winds: Saturday E-S 10-20 kt, Sunday NW-NE 5-15 kt. Outflow wind gusts to 25-40 kt with storms Sat/Sun, creating potential for blowing dust.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.