Climate averages 1991–2020
Boise weather
by month.
See how the year changes. July has the highest average daily maximum; July has the lowest average monthly rainfall.
Pleasant-weather months by our simple rule: MayJuneSeptember
Long-term climate patterns, not a forecast for a particular trip.
Across the year Boise averages a daytime high of 17.3°C and a nighttime low of 5.8°C, with about 311 mm of rain on roughly 68 days. July is the warmest month (average high 32.7°C) and December the coolest (3.7°C). December is the wettest month with 50 mm; July is the driest with 2.6 mm.
Months with pleasant weather by a simple rule (average high between 18°C and 29°C, average low of at least 5°C and at most 8 rain days): May, June and September. This looks at temperature and rain only, not humidity, wind, sea temperature or crowds.
The annual picture
A year in Boise
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Boise climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 3.8°C-4.6°C | -4.6°C | 45 | 9.5 | 9.39 h |
| February | 6.8°C-2.5°C | -2.5°C | 31 | 7.7 | 10.510 h |
| March | 11.9°C0.9°C | 0.9°C | 36 | 8.9 | 11.912 h |
| April | 15.9°C3.8°C | 3.8°C | 31 | 7.2 | 13.413 h |
| May | 21.6°C8.5°C | 8.5°C | 31 | 5.9 | 14.715 h |
| June | 26.5°C13.0°C | 13.0°C | 16 | 3.2 | 15.415 h |
| July | 32.7°C17.9°C | 17.9°C | 2.6 | 0.9 | 15.115 h |
| August | 31.9°C17.4°C | 17.4°C | 3.3 | 0.7 | 14.014 h |
| September | 26.2°C12.6°C | 12.6°C | 10 | 2.2 | 12.613 h |
| October | 17.7°C6.3°C | 6.3°C | 22 | 4.3 | 11.111 h |
| November | 9.3°C0.2°C | 0.2°C | 34 | 7.9 | 9.710 h |
| December | 3.7°C-4.1°C | -4.1°C | 50 | 10.1 | 9.09 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
Nearby cities
- MeridianUnited States · 15 kmHigh 17.4°C · Low 5.8°C · 279 mm rain a year
- NampaUnited States · 30 kmHigh 18.0°C · Low 6.7°C · 279 mm rain a year
- KennewickUnited States · 370 kmHigh 19.2°C · Low 7.8°C · 228 mm rain a year
- Tri-CitiesUnited States · 376 kmHigh 19.4°C · Low 7.9°C · 228 mm rain a year
- MissoulaUnited States · 401 kmHigh 13.4°C · Low 3.1°C · 508 mm rain a year
- BendUnited States · 413 kmHigh 14.2°C · Low 2.3°C · 544 mm rain a year
- OgdenUnited States · 437 kmHigh 15.4°C · Low 3.8°C · 503 mm rain a year
- LaytonUnited States · 449 kmHigh 15.2°C · Low 3.8°C · 474 mm rain a year
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsWhat do the high and low temperatures mean?
We average the daily maximum and daily minimum for each calendar month over 1991–2020. They are not record extremes, a forecast range or temperatures at a fixed time of day.
How is a rain day counted?
A local calendar day (standard time, UTC-7, no daylight saving) with at least 1 mm of total precipitation counts as one rain day. We count these for each year and month, then average across 30 years. The average does not predict which days will be wet.
Where do the numbers come from?
ERA5-Land (temperature) and ERA5 (precipitation) reanalysis from the Copernicus Climate Change Service, read from the Open-Meteo open-data archive. Temperature comes from the 0.1° model cell at 43.60°, -116.20° (2 km from the city centre), adjusted up by 0.9°C for the difference between the city's elevation (834 m) and the cell's (968 m). Rain comes from the 0.25° cell at 43.50°, -116.25°. These are model estimates, not weather-station readings; coast, hills and city streets can differ.
Does this page show sunshine, humidity or sea temperature?
No. The data used here contain air temperature and precipitation only. Daylight hours are calculated from the city's latitude (sunrise to sunset), not measured sunshine.