Boise weather in September
September in Boise: warm, dry, with clean air — one of the best months to visit.
#2 of 12 months in Boise · #27 of 604 destinations to visit in September · comfort 92/100 (tier S)
Updated June 2026 · climate normals from ERA5 reanalysis
Boise climate normals — September
| Daytime high | 28°C / 83°F | 🌤 warm |
|---|---|---|
| Nighttime low | 14°C / 56°F | |
| Feels like (high) | 26°C / 79°F | |
| Rainfall | 10 mm / 0.4 in | ☀️ dry |
| Rainy days | 2 days | |
| Humidity | 40% | 🍃 comfortable |
| Dew point | 5°C / 41°F | |
| Sunshine | 11.1 h/day | |
| Daylight | 12.5 h | |
| Wind | 17 km/h / 11 mph | |
| Air quality (US AQI) | 40 | 🍃 good |
Monthly averages from ERA5 reanalysis. AQI is the mean US Air Quality Index for the month.
Where is Boise?
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Boise in September — FAQ
- Is September a good time to visit Boise?
- September in Boise: warm, dry, with clean air — one of the best months to visit. It ranks #2 of 12 months for Boise on SeasonMap's comfort score (92/100).
- What is the weather like in Boise in September?
- In September, Boise averages a daily high of 28.2°C and a low of 13.5°C, with about 10.4 mm of rain over roughly 2.2 rainy days.
- What is the air quality in Boise in September?
- Boise has a mean US Air Quality Index of about 40 in September.