Boise weather by month
Boise runs from about -1°C in January to 28°C in July, with February the wettest month at 88 mm.
warmest month
July
28°C
coolest month
January
-1°C
wettest month
February
88 mm
worst air month
January
10 µg/m³
The whole year, month by month.
| Month | Avg temp | Rain | Sun | PM2.5 |
|---|---|---|---|---|
| January | -1°C | 87 mm | 159 h | 10 |
| February | 4°C | 88 mm | 193 h | 8 |
| March | 5°C | 61 mm | 301 h | 7 |
| April | 10°C | 43 mm | 349 h | 6 |
| May | 14°C | 35 mm | 398 h | 5 |
| June | 21°C | 13 mm | 411 h | 5 |
| July | 28°C | 2 mm | 433 h | 5 |
| August | 25°C | 2 mm | 402 h | 8 |
| September | 20°C | 6 mm | 330 h | 9 |
| October | 13°C | 15 mm | 292 h | 5 |
| November | 4°C | 59 mm | 188 h | 7 |
| December | 2°C | 81 mm | 179 h | 6 |
About 3,635 hours of sun a year. Roughly 50 rainy days a year.
These are long-run climate normals, not a forecast. A given year can sit well outside them. PM2.5 is a global model: near the coast it counts sea salt as fine particulate and reads high against ground stations, sometimes by a factor of two. Use the shape of the year, not the absolute number.
where these numbers come from
- · Temperature, rainfall and sunshine: ECMWF ERA5 reanalysis climate normals via Open-Meteo (CC BY 4.0), fetched once and stored.
- · PM2.5: Copernicus CAMS reanalysis, monthly means. Modelled, not station readings; near coasts CAMS counts sea salt as PM2.5 and reads high.
Last reviewed 2026-05-24. Full method, licences and the list of sources we rejected are on the methodology page.