| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 21°F | 37°F | 28°F | 2.0" |
| February | 21°F | 38°F | 29°F | 1.6" |
| March | 29°F | 49°F | 39°F | 2.9" |
| April | 40°F | 63°F | 51°F | 3.1" |
| May | 49°F | 72°F | 60°F | 4.2" |
| June | 58°F | 79°F | 68°F | 4.2" |
| July | 61°F | 83°F | 72°F | 4.1" |
| August | 59°F | 81°F | 69°F | 3.6" |
| September | 53°F | 75°F | 63°F | 3.3" |
| October | 44°F | 64°F | 53°F | 3.6" |
| November | 33°F | 52°F | 42°F | 2.2" |
| December | 26°F | 41°F | 33°F | 3.1" |
| Index | Defiance | Pennsylvania | National |
| Air quality index | 41 | 45 | 42 |
| Pollution index | 1,656,460 | 4,584,805 | 2,726,193 |
| Measurement | Total |
| Days measured | 354 |
| Days with good air quality | 281 |
| Days with moderate air quality | 73 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.005% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.004% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Saltillo, PA | 355 | 36 | 28.0% |
| Three Springs, PA | 592 | 36 | 28.0% |
| Valley-Hi, PA | 2 | 36 | 28.0% |
| Bedford, PA | 2,703 | 36 | 28.0% |
| St. Clairsville, PA | 67 | 39 | 22.0% |
| Defiance, PA | 481 | 41 | 18.0% |
| City | Population | Air Quality Index | National Avg. |
| Pleasant Groves, AL | 481 | 44 | 12.0% |
| Newell, CA | 481 | 29 | 42.0% |
| Manilla, IN | 481 | 28 | 44.0% |
| Kensington, KS | 481 | 19 | 62.0% |
| Scandia, KS | 481 | 32 | 36.0% |
| Defiance, PA | 481 | 41 | 18.0% |
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