textproduct: Boise

KEY MESSAGES

- A 15 to 20 percent chance of thunderstorms near the Idaho/Nevada border this afternoon.

- Fire weather concerns increase due to threat of thunderstorms Thursday afternoon through Friday.

- Thunderstorms with heavy rain may also increase the risk for flash flooding especially for recent burn scars on Friday and Saturday.

- Temperatures cooling to around 5 degrees below normal come Friday.

SHORT TERM /Tonight through Friday Night/

An increasingly active convective pattern is expected across southeast Oregon and southwest Idaho as monsoonal moisture continues to push northward into the region. For this afternoon and evening, isolated thunderstorms will focus near the Idaho/Nevada border. Mid-level moisture ahead of a weak trough to the north may also allow isolated convection (15% chance) late this evening from Burns to Baker City and McCall. Gusty outflow winds and lightning will be the main threats with early activity due to dry air in the lower boundary layer.

Moisture advection accelerates on Thursday supported by a passing upper-level shortwave. This feature will provide additional lift and support scattered thunderstorm development from Thursday afternoon through Friday morning across southwest Idaho and eastern Oregon. This increases the risk for new fire starts with abundant lightning associated with initially dry thunderstorms.

By Friday afternoon, deep monsoonal moisture fully encompasses much of Idaho in southwest flow aloft. Precipitable water values will climb significantly, with the highest values and best dynamic forcing concentrated over central Idaho. Convective hazards will transition from dry lightning and gusty winds to heavy rain production. These thunderstorms will create an elevated risk for flash flooding and debris flows, particularly over steep terrain and recent burn scars, including the Wapiti burn scar. A Flash Flood Watch may be needed for Friday and Saturday for burn scars in central Idaho as confidence in heavy rainfall potential increases. Increased cloud coverage and showers will also yield cooler temperatures Friday, dropping high temperatures several degrees below seasonal averages.

LONG TERM /Saturday through Wednesday/

Scattered showers and thunderstorms will continue into Saturday as moisture remains under persistent southwest flow aloft while another shortwave rotates through the area. Precipitable water values will remain high (near the 80th to 90th percentile), so the risk for localized flash flooding over recent burn scars across central Idaho will persist through Saturday afternoon. A warming and drying trend is expected to take hold Sunday and Monday as weak upper-level ridging attempts to build into the Intermountain West. Moisture will begin to scour out from west to east, though lingering low-level moisture will maintain a slight chance (10 to 20 percent) of afternoon showers and thunderstorms over higher terrain. Temperatures will recover back toward seasonal normals for early next week. Model guidance suggests another Pacific trough approaching the northwest coast by midweek, which could reintroduce breezy conditions, a slight cooling trend, and increasing precipitation chances.

AVIATION /18Z Wednesday through Thursday/

Issued 1159 AM MDT WED AUG 12 2026 Generally VFR with some periods of MVFR possible in wildfire smoke. A 15-20% chance of showers and thunderstorms south of KTWF through this evening. High density altitude this afternoon due to heat. Surface winds: W-NW 10-20 kt this afternoon. Winds aloft at 10kft MSL: W-SW 5-15 kt.

KBOI...VFR with reduction in visibility due to wildfire smoke at times. Foothills obscured by smoke.. High density altitude this afternoon due to heat. Surface winds: NW 7-12 kt with gusts up to 18 kt in the afternoon.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Red Flag Warning from 3 PM Thursday to 6 AM MDT Friday for IDZ400>403-420-421-423-424-426. OR...Red Flag Warning from 2 PM Thursday to 5 AM PDT Friday for ORZ670>672. Air Quality Alert until 1 PM MDT /noon PDT/ Friday for ORZ061- 063-064. Red Flag Warning from 3 PM MDT /2 PM PDT/ Thursday to 9 AM MDT /8 AM PDT/ Friday for ORZ673>675.