Idaho local data guide

Boise Summer Humidity Characteristics

Boise, Idaho experiences exceptionally low relative humidity during the summer months, reflecting its semi-arid high-desert climate. While morning humidity levels hover between 40% and 55%, relative humidity drops sharply to 15%–30% in the afternoon as temperatures peak.

Updated with grounded research as of 2026-07-29.

The short answer

In Boise, Idaho, summer relative humidity levels typically average around 30% monthly, with afternoon readings routinely dropping to 15%–30% when temperatures peak.

Key facts

Average Afternoon Humidity
15% to 25%
Average Morning Humidity
40% to 55%
Monthly Average Relative Humidity (July/August)
30%
NOAA Climate Normals Period
1991–2020

Diurnal Moisture Variations in the Treasure Valley

In Boise, Idaho, relative humidity follows a pronounced daily cycle tied closely to local high-desert air temperatures. During cool early summer mornings around sunrise, relative humidity peaks between 40% and 55%. As solar heating intensifies through late afternoon, the relative humidity regularly plummets to between 15% and 30% across the Treasure Valley.

  • Morning relative humidity: 40%–55% during cool early hours.
  • Afternoon relative humidity: 15%–30% during daily temperature peaks.
  • Overall summer monthly average humidity: ~30% in July and August.

Impact on Housing and Daily Comfort

Low humidity levels significantly enhance human thermal comfort during hot Boise summer days. High temperatures reaching into the 90s and 100s feel substantially less oppressive than in humid regions because sweat evaporates rapidly from the skin, enabling efficient natural cooling.

  • Evaporative cooling and swamp coolers operate with high efficiency in low-humidity air.
  • Rapid nighttime cooling allows homes to dump excess heat quickly when evening winds kick in.
  • Lower interior humidity reduces risks of mold growth inside residential properties.

Summer Weather Events and Anomalies

While dry conditions dominate the summer season, occasional influxes of monsoonal moisture from the desert Southwest can briefly alter Boise's atmosphere. These events can trigger localized afternoon dry thunderstorms, temporary humidity spikes, and gusty outflow winds.

  • Monsoonal pushes can temporarily push afternoon relative humidity above 40%.
  • Dry lightning during low-humidity windows creates heightened seasonal wildfire risks.

Common questions

Is Boise, Idaho considered humid during summer?

No. Boise features a semi-arid climate where summer afternoons typically see relative humidity fall to between 15% and 30%, resulting in dry heat.

How does low humidity affect home cooling in Boise?

Low humidity makes air conditioning highly effective and allows dry-climate options like evaporative cooling (swamp coolers) to function efficiently during hot summer afternoons.

Related Idaho questions

  • What is the average summer temperature in Boise, Idaho?
  • How does summer air quality in Boise affect outdoor activities?
  • What climate zone is Boise, Idaho classified under?

Sources and verification