| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 36°F | 61°F | 47°F | 1.6" |
| February | 40°F | 66°F | 51°F | 1.5" |
| March | 49°F | 73°F | 59°F | 1.8" |
| April | 56°F | 79°F | 66°F | 2.6" |
| May | 62°F | 84°F | 72°F | 5.1" |
| June | 69°F | 90°F | 79°F | 2.0" |
| July | 71°F | 93°F | 81°F | 1.4" |
| August | 71°F | 94°F | 82°F | 3.2" |
| September | 65°F | 88°F | 75°F | 3.8" |
| October | 56°F | 80°F | 67°F | 3.1" |
| November | 47°F | 70°F | 57°F | 1.9" |
| December | 39°F | 62°F | 49°F | 1.3" |
| Index | Harper | Texas | National |
| Air quality index | 49 | 52 | 42 |
| Pollution index | 1,877,920 | 2,009,300 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 196 |
| Days with moderate air quality | 163 |
| Days w/ poor A.Q. for sensitive groups | 5 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.001% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Harper, TX | 1,391 | 49 | 2.0% |
| City | Population | Air Quality Index | National Avg. |
| Dunnigan, CA | 1,391 | 44 | 12.0% |
| Hagan, GA | 1,391 | 39 | 22.0% |
| Woodbine, IA | 1,391 | 40 | 20.0% |
| Owensville, IN | 1,391 | 45 | 10.0% |
| Humansville, MO | 1,391 | 39 | 22.0% |
| Harper, TX | 1,391 | 49 | 2.0% |
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