textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Isolated showers and thunderstorms today and Monday favoring higher terrain, with outflows up to 40 mph and local downpours.

- Temperatures near or slightly above normal through mid-week, then further warming expected by late week.

- Return of monsoon moisture Friday into the weekend will increase shower and thunderstorm chances once again.

SHORT TERM /Through Tuesday Night/

Issued 208 PM MDT SUN AUG 16 2026 An upper level ridge centered over the Intermountain West will maintain warmer and drier conditions across southeast Oregon and southwest Idaho through the short term period under southwesterly flow aloft. Mid-level moisture streaming around the western periphery of this ridge will interact with weak instability today, generating isolated afternoon and evening thunderstorms. The highest confidence for storm development today remains focused over the higher terrain of southwest Idaho, including the Owyhee Mountains and West Central Mountains. With low levels remaining quite dry, main threats with today's storms will be localized gusty outflow winds up to 45 mph and brief dry lightning strikes.

A weak shortwave trough is shown to move inland across the forecast area on Monday bringing mid-level Pacific moisture. Although this moisture is not as extensive as the monsoonal moisture from the previous couple of days, the incoming dynamic support, combined with daytime heating, should be sufficient to support isolated thunderstorm development across the area Monday afternoon and evening. Given the limited low-level moisture, storms are likely to produce gusty outflow winds 35 to 45 mph, along with frequent lightning and little to no rainfall increasing the risk for further fire starts.

Another trough passage on Tuesday should briefly suppress the ridge for slightly cooler temperatures, though still above normal and breezy conditions. Cooler air aloft and lingering mid-level moisture will maintain a slight chance of afternoon mountain thunderstorms, mainly over the Central Idaho Mountains, but overall coverage will decrease compared to Monday. Temperatures throughout the short term will remain roughly 5 degrees above seasonal averages.

LONG TERM /Wednesday through Sunday/

Issued 208 PM MDT SUN AUG 16 2026 As the Desert Southwest upper-level ridge builds Wednesday, temperatures will be near normal under dry conditions. Starting Thursday, flow aloft will be shifting from southwesterly to southerly as a Pacific low pressure system moves closer to shore. This will increase precipitation chances Thursday and further Friday, primarily over higher terrain. Temperatures will become hot Thursday and Friday under this pattern. Late Friday into the weekend, the trough will move onshore and then northeast across the Pacific Northwest states. Showers and thunderstorm chances will persevere as the trough enhances large-scale lift and carries moisture. Several degrees of cooling will be likely for Saturday and Sunday.

AVIATION /00Z Monday through Tuesday/

Issued 531 PM MDT SUN AUG 16 2026 Generally VFR with increasing high clouds and isolated showers/thunderstorms this evening. Storms will be most prevalent along higher terrain from KBKE eastward to KMYL and the central mountains of Idaho...as well as south central Idaho. The strongest storms could produce wind gusts to 30 kt, but should dissipate around sunset. Increasing threat of thunderstorms for Monday afternoon area-wide, with isolated to scattered storms in the forecast after 20Z. Surface winds SW to NW 8 to 15 kt, becoming variable less than 10 kt overnight. Increasing from the SW to NW Monday afternoon. Winds aloft above 10kft AGL: SW 15-25 kt.

KBOI...VFR. Stray shower possible through 03Z, less than 15% chance. Potential for showers/thunderstorms Monday afternoon and evening after 20Z...probability of thunder around 10%. Surface winds NW around 10 kt, becoming SE less than 10 kt overnight. Winds aloft above 10kft ALL: SW 15-25 kt.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.