| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 26°F | 44°F | 34°F | 3.3" |
| February | 26°F | 46°F | 35°F | 2.6" |
| March | 33°F | 56°F | 44°F | 3.6" |
| April | 44°F | 68°F | 56°F | 4.0" |
| May | 54°F | 77°F | 65°F | 3.9" |
| June | 64°F | 86°F | 74°F | 4.8" |
| July | 70°F | 90°F | 79°F | 5.0" |
| August | 68°F | 87°F | 77°F | 5.8" |
| September | 61°F | 82°F | 71°F | 4.3" |
| October | 50°F | 70°F | 59°F | 4.7" |
| November | 39°F | 59°F | 48°F | 2.8" |
| December | 31°F | 49°F | 40°F | 4.7" |
| Index | Williamstown | New Jersey | National |
| Air quality index | 40 | 45 | 42 |
| Pollution index | 4,933,660 | 7,246,891 | 2,726,193 |
| Measurement | Total |
| Days measured | 361 |
| Days with good air quality | 297 |
| Days with moderate air quality | 61 |
| Days w/ poor A.Q. for sensitive groups | 3 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.080% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.004% |
| Lead | 0.030% |
| Mercury | 0.360% |
| City | Population | Air Quality Index | National Avg. |
| Folsom, NJ | 1,610 | 40 | 20.0% |
| Buena, NJ | 4,323 | 40 | 20.0% |
| Olivet, NJ | 1,322 | 40 | 20.0% |
| Chesilhurst, NJ | 1,440 | 40 | 20.0% |
| Glassboro, NJ | 20,069 | 40 | 20.0% |
| Williamstown, NJ | 14,161 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Greendale, WI | 14,160 | 44 | 12.0% |
| Anna, TX | 14,159 | 51 | 2.0% |
| Weigelstown, PA | 14,156 | 41 | 18.0% |
| Washington Court House, OH | 14,155 | 38 | 24.0% |
| Hockessin, DE | 14,172 | 51 | 2.0% |
| Williamstown, NJ | 14,161 | 40 | 20.0% |
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