| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 25°F | 39°F | 32°F | 8.6" |
| February | 19°F | 35°F | 27°F | 2.8" |
| March | 32°F | 52°F | 41°F | 7.3" |
| April | 40°F | 63°F | 51°F | 6.0" |
| May | 48°F | 75°F | 62°F | 4.9" |
| June | 61°F | 84°F | 73°F | 6.4" |
| July | 63°F | 85°F | 74°F | 6.1" |
| August | 65°F | 87°F | 75°F | 8.0" |
| September | 56°F | 81°F | 68°F | 6.4" |
| October | 48°F | 67°F | 57°F | 4.5" |
| November | 34°F | 54°F | 44°F | 4.0" |
| December | 24°F | 38°F | 31°F | 3.4" |
| Index | Westerville | Ohio | National |
| Air quality index | 46 | 40 | 42 |
| Pollution index | 21,574,800 | 4,472,386 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 237 |
| Days with moderate air quality | 127 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.030% |
| Benzene | 0.230% |
| Carbon Tetrachloride | 0.100% |
| Lead | 0.190% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Hartford, OH | 355 | 41 | 18.0% |
| Centerburg, OH | 1,930 | 41 | 18.0% |
| Delaware, OH | 41,818 | 46 | 8.0% |
| Gahanna, OH | 35,442 | 46 | 8.0% |
| Johnstown, OH | 5,149 | 46 | 8.0% |
| Westerville, OH | 40,443 | 46 | 8.0% |
| City | Population | Air Quality Index | National Avg. |
| Lancaster, OH | 40,438 | 46 | 8.0% |
| Huber Heights, OH | 40,465 | 47 | 6.0% |
| Covington, KY | 40,466 | 54 | 8.0% |
| Wentzville, MO | 40,407 | 54 | 8.0% |
| New Tecumseth, ON | 40,488 | n/a | |
| Westerville, OH | 40,443 | 46 | 8.0% |
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