| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 28°F | 46°F | 36°F | 2.6" |
| February | 29°F | 49°F | 38°F | 2.2" |
| March | 37°F | 58°F | 46°F | 3.4" |
| April | 47°F | 70°F | 57°F | 3.8" |
| May | 57°F | 76°F | 66°F | 4.4" |
| June | 66°F | 85°F | 75°F | 4.8" |
| July | 71°F | 89°F | 79°F | 3.5" |
| August | 69°F | 87°F | 77°F | 3.1" |
| September | 62°F | 81°F | 71°F | 4.2" |
| October | 50°F | 70°F | 59°F | 4.3" |
| November | 39°F | 59°F | 48°F | 2.8" |
| December | 32°F | 50°F | 40°F | 3.4" |
| Index | Dumfries | Virginia | National |
| Air quality index | 47 | 58 | 42 |
| Pollution index | 520,936 | 1,561,881 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 209 |
| Days with moderate air quality | 145 |
| Days w/ poor A.Q. for sensitive groups | 10 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.020% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.050% |
| Mercury | 0.001% |
| City | Population | Air Quality Index | National Avg. |
| Manassas, VA | 41,038 | 47 | 6.0% |
| Stafford Courthouse, VA | 4,839 | 47 | 6.0% |
| Belle Haven, VA | 6,582 | 47 | 6.0% |
| Indian Head, MD | 3,803 | 47 | 6.0% |
| Cherry Hill, VA | 20,344 | 47 | 6.0% |
| Dumfries, VA | 5,559 | 47 | 6.0% |
| City | Population | Air Quality Index | National Avg. |
| Elburn, IL | 5,559 | 55 | 10.0% |
| Oxford, PA | 5,560 | 45 | 10.0% |
| West Modesto, CA | 5,557 | 49 | 2.0% |
| Belvedere, SC | 5,557 | 47 | 6.0% |
| Deer Park, OH | 5,561 | 54 | 8.0% |
| Dumfries, VA | 5,559 | 47 | 6.0% |
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