| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 10°F | 28°F | 19°F | 3.3" |
| February | 15°F | 34°F | 24°F | 1.6" |
| March | 22°F | 44°F | 33°F | 2.3" |
| April | 31°F | 55°F | 44°F | 3.6" |
| May | 38°F | 65°F | 54°F | 4.4" |
| June | 44°F | 75°F | 63°F | 3.2" |
| July | 52°F | 90°F | 75°F | 2.6" |
| August | 50°F | 83°F | 69°F | 2.6" |
| September | 39°F | 73°F | 58°F | 2.8" |
| October | 32°F | 59°F | 45°F | 3.6" |
| November | 23°F | 46°F | 34°F | 1.2" |
| December | 15°F | 30°F | 22°F | 1.7" |
| Index | Montpelier | Idaho | National |
| Air quality index | 44 | 32 | 42 |
| Pollution index | 1,218,100 | 2,063,710 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 272 |
| Days with moderate air quality | 79 |
| Days w/ poor A.Q. for sensitive groups | 14 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.003% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Georgetown, ID | 587 | 44 | 12.0% |
| Paris, ID | 667 | 44 | 12.0% |
| Bennington, ID | 94 | 44 | 12.0% |
| St. Charles, ID | 160 | 44 | 12.0% |
| Bloomington, ID | 204 | 44 | 12.0% |
| Montpelier, ID | 2,512 | 44 | 12.0% |
| City | Population | Air Quality Index | National Avg. |
| Dover-Foxcroft, ME | 2,512 | 31 | 38.0% |
| Pelican Rapids, MN | 2,512 | 33 | 34.0% |
| Farmington, MS | 2,512 | 37 | 26.0% |
| Highspire, PA | 2,512 | 44 | 12.0% |
| Calvert City, KY | 2,513 | 44 | 12.0% |
| Montpelier, ID | 2,512 | 44 | 12.0% |
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