| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 38°F | 55°F | 45°F | 6.9" |
| February | 41°F | 61°F | 50°F | 2.8" |
| March | 49°F | 71°F | 59°F | 14.0" |
| April | 53°F | 75°F | 63°F | 2.3" |
| May | 63°F | 82°F | 72°F | 6.7" |
| June | 72°F | 91°F | 80°F | 13.0" |
| July | 72°F | 92°F | 81°F | 10.5" |
| August | 74°F | 96°F | 84°F | 8.4" |
| September | 69°F | 92°F | 80°F | 11.0" |
| October | 57°F | 81°F | 67°F | 4.0" |
| November | 50°F | 72°F | 60°F | 7.2" |
| December | 37°F | 60°F | 47°F | 5.3" |
| Index | Terrell | Texas | National |
| Air quality index | 51 | 52 | 42 |
| Pollution index | 37,723,200 | 2,009,300 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 181 |
| Days with moderate air quality | 155 |
| Days w/ poor A.Q. for sensitive groups | 28 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.060% |
| Benzene | 0.290% |
| Carbon Tetrachloride | 0.220% |
| Lead | 0.230% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| Hawk Cove, TX | 427 | 51 | 2.0% |
| Quinlan, TX | 1,758 | 51 | 2.0% |
| Combine, TX | 2,535 | 51 | 2.0% |
| Kaufman, TX | 7,646 | 51 | 2.0% |
| Post Oak Bend City, TX | 515 | 51 | 2.0% |
| Terrell, TX | 18,513 | 51 | 2.0% |
| City | Population | Air Quality Index | National Avg. |
| Durant, OK | 18,516 | 325 | 550.0% |
| Russell, ON | 18,518 | n/a | |
| Brookfield, IL | 18,520 | 55 | 10.0% |
| Winchester, KY | 18,520 | 42 | 16.0% |
| Concord, MO | 18,521 | 54 | 8.0% |
| Terrell, TX | 18,513 | 51 | 2.0% |
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