| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 19°F | 35°F | 27°F | 2.3" |
| February | 20°F | 37°F | 28°F | 2.0" |
| March | 30°F | 50°F | 39°F | 2.5" |
| April | 40°F | 64°F | 51°F | 3.7" |
| May | 51°F | 74°F | 62°F | 3.7" |
| June | 61°F | 83°F | 71°F | 4.6" |
| July | 63°F | 85°F | 74°F | 4.0" |
| August | 61°F | 84°F | 72°F | 3.5" |
| September | 55°F | 78°F | 66°F | 2.9" |
| October | 44°F | 66°F | 54°F | 2.6" |
| November | 33°F | 53°F | 43°F | 2.5" |
| December | 25°F | 40°F | 32°F | 2.7" |
| Index | Tiffin | Ohio | National |
| Air quality index | 40 | 40 | 42 |
| Pollution index | 2,402,580 | 4,472,386 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 291 |
| Days with moderate air quality | 73 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.005% |
| Lead | 0.020% |
| Mercury | 0.003% |
| City | Population | Air Quality Index | National Avg. |
| Sycamore, OH | 740 | 39 | 22.0% |
| McCutchenville, OH | 211 | 39 | 22.0% |
| Carey, OH | 3,386 | 39 | 22.0% |
| New Riegel, OH | 329 | 40 | 20.0% |
| Bettsville, OH | 762 | 40 | 20.0% |
| Tiffin, OH | 17,473 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Centralia, WA | 17,473 | 20 | 60.0% |
| Hanover, MB | 17,472 | n/a | |
| Amesbury Town, MA | 17,474 | 37 | 26.0% |
| Brownsville, FL | 17,475 | 41 | 18.0% |
| Redland, MD | 17,475 | 47 | 6.0% |
| Tiffin, OH | 17,473 | 40 | 20.0% |
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