| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 29°F | 43°F | 36°F | 2.7" |
| February | 30°F | 45°F | 37°F | 7.4" |
| March | 37°F | 55°F | 45°F | 3.9" |
| April | 47°F | 67°F | 57°F | 2.4" |
| May | 57°F | 76°F | 66°F | 4.8" |
| June | 66°F | 84°F | 75°F | 8.6" |
| July | 71°F | 88°F | 79°F | 10.7" |
| August | 68°F | 85°F | 76°F | 8.2" |
| September | 62°F | 80°F | 71°F | 5.1" |
| October | 52°F | 68°F | 60°F | 4.5" |
| November | 41°F | 57°F | 49°F | 4.8" |
| December | 35°F | 48°F | 41°F | 3.2" |
| Index | Williston | Maryland | National |
| Air quality index | 36 | 43 | 42 |
| Pollution index | 1,358,370 | 5,342,367 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 303 |
| Days with moderate air quality | 61 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Blades, DE | 1,123 | 36 | 28.0% |
| Denton, MD | 4,488 | 36 | 28.0% |
| Bridgeville, DE | 3,508 | 36 | 28.0% |
| Farmington, DE | 184 | 36 | 28.0% |
| Greenwood, DE | 1,127 | 36 | 28.0% |
| Williston, MD | 174 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Gantt, AL | 174 | 35 | 30.0% |
| St. Stephens, AL | 174 | 42 | 16.0% |
| Antoine, AR | 174 | 32 | 36.0% |
| Red Rock CDP (Apache County), AZ | 174 | 47 | 6.0% |
| Fort Bidwell, CA | 174 | 29 | 42.0% |
| Williston, MD | 174 | 36 | 28.0% |
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