| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 14°F | 32°F | 22°F | 1.7" |
| February | 12°F | 32°F | 21°F | 3.0" |
| March | 21°F | 42°F | 30°F | 4.7" |
| April | 34°F | 56°F | 43°F | 7.1" |
| May | 44°F | 65°F | 53°F | 4.1" |
| June | 57°F | 78°F | 66°F | 7.3" |
| July | 61°F | 81°F | 70°F | 4.3" |
| August | 60°F | 83°F | 70°F | 4.3" |
| September | 55°F | 75°F | 64°F | 6.0" |
| October | 46°F | 62°F | 53°F | 14.4" |
| November | 31°F | 47°F | 38°F | 7.1" |
| December | 18°F | 34°F | 25°F | 3.8" |
| Index | Alton | New Hampshire | National |
| Air quality index | 31 | 34 | 42 |
| Pollution index | 4,139,320 | 3,959,618 | 2,726,193 |
| Measurement | Total |
| Days measured | 316 |
| Days with good air quality | 308 |
| Days with moderate air quality | 8 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.060% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.020% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Pittsfield, NH | 1,464 | 27 | 46.0% |
| Loudon, NH | 830 | 27 | 46.0% |
| Rochester, NH | 31,305 | 27 | 46.0% |
| Farmington, NH | 4,140 | 31 | 38.0% |
| Laconia, NH | 16,584 | 31 | 38.0% |
| Alton, NH | 170 | 31 | 38.0% |
| City | Population | Air Quality Index | National Avg. |
| White Mountain, AK | 170 | 38 | 24.0% |
| Palominas, AZ | 170 | 45 | 10.0% |
| Santa Claus, GA | 170 | 26 | 48.0% |
| Haverhill, IA | 170 | 37 | 26.0% |
| Webster, IA | 170 | 35 | 30.0% |
| Alton, NH | 170 | 31 | 38.0% |
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