| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 17°F | 35°F | 26°F | 2.3" |
| February | 17°F | 36°F | 26°F | 2.7" |
| March | 25°F | 45°F | 34°F | 3.4" |
| April | 36°F | 59°F | 47°F | 3.6" |
| May | 46°F | 70°F | 57°F | 3.6" |
| June | 54°F | 77°F | 65°F | 4.8" |
| July | 61°F | 83°F | 71°F | 3.9" |
| August | 58°F | 81°F | 69°F | 4.0" |
| September | 52°F | 74°F | 62°F | 3.4" |
| October | 41°F | 62°F | 51°F | 4.5" |
| November | 32°F | 50°F | 41°F | 3.3" |
| December | 23°F | 39°F | 30°F | 3.5" |
| Index | Somersworth | New Hampshire | National |
| Air quality index | 37 | 34 | 42 |
| Pollution index | 91,790 | 3,959,618 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 353 |
| Days with moderate air quality | 12 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.002% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.001% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Rochester, NH | 31,988 | 27 | 46.0% |
| Berwick, ME | 2,058 | 27 | 46.0% |
| Farmington, NH | 4,278 | 31 | 38.0% |
| Milton, NH | 549 | 31 | 38.0% |
| South Eliot, ME | 3,168 | 37 | 26.0% |
| Somersworth, NH | 12,381 | 37 | 26.0% |
| City | Population | Air Quality Index | National Avg. |
| Babylon, NY | 12,378 | 51 | 2.0% |
| Rossmoor, CA | 12,384 | 72 | 44.0% |
| Sidney, BC | 12,386 | n/a | |
| Neosho, MO | 12,375 | 37 | 26.0% |
| Lantana, FL | 12,390 | 36 | 28.0% |
| Somersworth, NH | 12,381 | 37 | 26.0% |
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