| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 17°F | 36°F | 26°F | 3.0" |
| February | 17°F | 38°F | 27°F | 2.8" |
| March | 26°F | 47°F | 36°F | 3.4" |
| April | 37°F | 63°F | 49°F | 4.1" |
| May | 47°F | 73°F | 59°F | 4.0" |
| June | 56°F | 80°F | 68°F | 5.8" |
| July | 62°F | 86°F | 73°F | 4.8" |
| August | 59°F | 84°F | 71°F | 4.4" |
| September | 53°F | 77°F | 64°F | 3.7" |
| October | 42°F | 65°F | 52°F | 5.9" |
| November | 31°F | 53°F | 41°F | 3.0" |
| December | 23°F | 41°F | 32°F | 4.2" |
| Index | Westfield | Massachusetts | National |
| Air quality index | 40 | 40 | 42 |
| Pollution index | 7,859,360 | 8,399,610 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 305 |
| Days with moderate air quality | 59 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.030% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.030% |
| Lead | 0.320% |
| Mercury | 0.070% |
| City | Population | Air Quality Index | National Avg. |
| Chester, MA | 935 | 37 | 26.0% |
| Sherwood Manor, CT | 5,901 | 40 | 20.0% |
| Agawam Town, MA | 28,627 | 40 | 20.0% |
| West Springfield Town, MA | 28,527 | 40 | 20.0% |
| Northampton, MA | 28,552 | 40 | 20.0% |
| Westfield, MA | 41,303 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Bremerton, WA | 41,258 | 18 | 64.0% |
| Belleville, IL | 41,256 | 54 | 8.0% |
| Greenacres, FL | 41,242 | 36 | 28.0% |
| Moline, IL | 41,213 | 46 | 8.0% |
| Grove City, OH | 41,394 | 46 | 8.0% |
| Westfield, MA | 41,303 | 40 | 20.0% |
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