Idaho local data guide

Boise, Idaho Weather in August

August in Boise is characterized by a hot, dry, high-desert climate. Long-term climate normals show daily high temperatures typically in the low-to-mid 90s°F, with nights providing a cooler respite. Precipitation is minimal, making it one of the driest months of the year.

Updated with grounded research as of 2026-07-21.

The short answer

August in Boise, Idaho, is defined by its hot, high-desert climate, featuring significant diurnal temperature swings where daytime highs reach the low-to-mid 90s°F while nighttime lows drop into the 60s°F. The region experiences very low humidity and minimal precipitation, making it one of the driest times of the year, though residents should remain aware of potential wildfire smoke impacts from the broader Pacific Northwest region.

Key facts

Average High Temperature
~89°F – 91°F
Average Low Temperature
~58°F – 62°F
Average Monthly Precipitation
~0.17 – 0.28 inches

High Desert Climate Dynamics

Boise’s location in the Treasure Valley, surrounded by mountain ranges, creates a semi-arid, high-desert environment. A defining characteristic of this geography is the significant diurnal temperature variation; the dry air allows the region to heat up quickly during the day and cool down rapidly once the sun sets.

  • Daytime highs frequently reach the 90s°F, with occasional days exceeding 100°F.
  • Nighttime temperatures provide relief, typically dropping into the low 60s°F.
  • Relative humidity is often below 20% during summer afternoons, contributing to the 'dry heat' experience.

Precipitation and Humidity

August is historically one of the driest months of the year in Boise. Rainfall is rare, and the low humidity levels mean that perspiration evaporates efficiently, though prolonged exposure to high heat still necessitates caution and hydration.

  • Average precipitation is minimal, generally measuring less than 0.3 inches for the entire month.
  • The lack of moisture in the air limits cloud cover, resulting in long, sunny days.

Air Quality and Wildfire Considerations

While Boise enjoys abundant sunshine, late summer occasionally brings wildfire smoke from fires burning in Idaho or neighboring states. Because of the valley’s topography, smoke can sometimes become trapped, leading to temporary periods of degraded air quality.

  • Monitor the Air Quality Index (AQI) via official state resources during August.
  • Sensitive groups should plan to limit strenuous outdoor activity if smoke levels rise.
  • Local fire restrictions are often in effect through mid-October to mitigate wildfire risk.

Common questions

Is it humid in Boise in August?

No, Boise has a very dry climate. In the summer, relative humidity often drops below 20% during the afternoon, which makes high temperatures feel more manageable than they would in more humid climates.

Should I be concerned about wildfire smoke?

While not every August is smoky, the late summer season is when wildfire risk is typically highest across the Western U.S. It is common for smoke to drift into the Treasure Valley depending on wind patterns and the intensity of nearby fire seasons. Residents should check the Idaho Department of Environmental Quality's smoke map for real-time air quality updates.

Related Idaho questions

  • What is the wildfire smoke season in Boise?
  • What is the typical humidity in Boise during summer?
  • When is the best time to visit Boise for outdoor activities?

Sources and verification