| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 7°F | 28°F | 17°F | 1.4" |
| February | 8°F | 29°F | 18°F | 1.6" |
| March | 17°F | 39°F | 28°F | 2.0" |
| April | 31°F | 54°F | 42°F | 2.9" |
| May | 42°F | 67°F | 54°F | 4.2" |
| June | 51°F | 73°F | 62°F | 5.1" |
| July | 55°F | 78°F | 67°F | 5.3" |
| August | 53°F | 76°F | 64°F | 4.7" |
| September | 46°F | 70°F | 57°F | 3.2" |
| October | 37°F | 57°F | 46°F | 4.3" |
| November | 26°F | 45°F | 34°F | 2.4" |
| December | 16°F | 32°F | 24°F | 3.0" |
| Index | Littleton | New Hampshire | National |
| Air quality index | 40 | 34 | 42 |
| Pollution index | 1,278,430 | 3,959,618 | 2,726,193 |
| Measurement | Total |
| Days measured | 324 |
| Days with good air quality | 314 |
| Days with moderate air quality | 10 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.010% |
| Mercury | 0.001% |
| City | Population | Air Quality Index | National Avg. |
| Woodsville, NH | 1,152 | 34 | 32.0% |
| Wells River, VT | 409 | 34 | 32.0% |
| Mountain Lakes, NH | 643 | 34 | 32.0% |
| St. Johnsbury, VT | 5,815 | 40 | 20.0% |
| Whitefield, NH | 1,202 | 40 | 20.0% |
| Littleton, NH | 4,294 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Argo, AL | 4,294 | 53 | 6.0% |
| Honesdale, PA | 4,294 | 38 | 24.0% |
| Spring Valley Village, TX | 4,294 | 52 | 4.0% |
| West Reading, PA | 4,293 | 42 | 16.0% |
| Roxton Pond, QC | 4,293 | n/a | |
| Littleton, NH | 4,294 | 40 | 20.0% |
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