textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Heat Advisory Thursday and Friday for lower elevations as temperatures push above 100 degrees.

- Increased chance of showers and thunderstorms over higher terrain Friday and Saturday.

- Above normal temperatures next week with a chance of thunderstorms over the mountains of southwest Idaho.

SHORT TERM /Through Friday Night/

Issued 418 AM MDT WED AUG 19 2026 Next few days will see heat build over the region as the Desert SW ridge expands northward. Guidance has edged higher over the past 24h, pushing more lower elevation sites in the 98-104 range for Thur/Fri. Certainly 850-700 thickness values would support hotter temperatures than NBM has for these days so have trended the forecast highs warmer, especially on Friday which will be the hottest day. Resulting highs and overnight lows (Thursday night) supported issuance of a Heat Advisory Thur/Fri across the Snake Plain and Weiser Basin. Otherwise looking at dry conditions across the area today. The building upper ridge will push monsoon moisture back to the ID/NV border on Thursday, then northward through into w-central Idaho on Friday, resulting in a chance of thunderstorms each afternoon. Precipitation chances have increased to 30-50% for Friday/Friday night across the western Magic Valley and eastern Boise mtns. The initial push of thunderstorms will likely produce more wind than rain on Friday as the near surface layer is fairly dry.

LONG TERM /Saturday through Wednesday/

Issued 418 AM MDT WED AUG 19 2026 An upper trough will enter the Pac NW on Saturday, tracking northeastward into Canada by Sunday. Gusty southwest winds develop across open terrain in SE Oregon and SW Idaho south of the Snake Plain on Saturday bringing elevated fire weather conditions. Forecast temperatures have continued to edge warmer for Saturday as guidance is delaying a frontal passage until the late afternoon/evening. Seeing a growing number solutions keep lower elevations in the upper 90s, which is warmer than the current NBM. Increased moisture aloft (precipitable water values reaching the 80th percentile) will support a 20-50% chance of afternoon/evening thunderstorms over w-central and s-central ID and the mtns of Baker County. Gusty winds and brief heavy rain could accompany storms.

The remainder of the extended period will be defined by the persistent Four Corners ridge which will place our region under southwest flow. Near normal temperatures Sunday, will be on the rise next week as the ridge rebounds. Moisture circling the ridge will keep a chance of afternoon thunderstorms mostly across SW Idaho zones.

AVIATION /12Z Wednesday through Thursday/

Issued 547 AM MDT WED AUG 19 2026 VFR under mostly clear skies. Increasing wildfire smoke across NE Oregon this afternoon. Surface winds: less than 10kt through tonight. Winds aloft at 10kft MSL: SW-W 5-15 kt.

KBOI...VFR under mostly clear skies. Light surface winds through Wednesday.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Heat Advisory from noon Thursday to 9 PM MDT Friday for IDZ012- 014-016-033. OR...Heat Advisory from noon MDT /11 AM PDT/ Thursday to 9 PM MDT /8 PM PDT/ Friday for ORZ064.