| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 19°F | 39°F | 29°F | 2.7" |
| February | 19°F | 40°F | 29°F | 3.0" |
| March | 28°F | 49°F | 38°F | 3.5" |
| April | 38°F | 62°F | 50°F | 4.0" |
| May | 48°F | 73°F | 60°F | 3.3" |
| June | 57°F | 79°F | 68°F | 5.0" |
| July | 63°F | 85°F | 74°F | 3.9" |
| August | 60°F | 82°F | 71°F | 4.1" |
| September | 54°F | 77°F | 65°F | 3.7" |
| October | 43°F | 66°F | 54°F | 4.4" |
| November | 33°F | 54°F | 43°F | 3.4" |
| December | 26°F | 44°F | 34°F | 4.0" |
| Index | Norwich | Connecticut | National |
| Air quality index | 37 | 43 | 42 |
| Pollution index | 2,806,150 | 8,629,883 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 323 |
| Days with moderate air quality | 34 |
| Days w/ poor A.Q. for sensitive groups | 7 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.004% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.040% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Willimantic, CT | 18,669 | 33 | 34.0% |
| South Windham, CT | 1,475 | 33 | 34.0% |
| Colchester, CT | 5,147 | 33 | 34.0% |
| South Coventry, CT | 1,413 | 33 | 34.0% |
| Wauregan, CT | 1,486 | 33 | 34.0% |
| Norwich, CT | 39,112 | 37 | 26.0% |
| City | Population | Air Quality Index | National Avg. |
| Duncanville, TX | 39,096 | 51 | 2.0% |
| South Valley, NM | 39,150 | 53 | 6.0% |
| French Valley, CA | 39,057 | 89 | 78.0% |
| Germantown, TN | 39,196 | 45 | 10.0% |
| Northglenn, CO | 39,201 | 58 | 16.0% |
| Norwich, CT | 39,112 | 37 | 26.0% |
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