| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 24°F | 46°F | 34°F | 2.7" |
| February | 25°F | 48°F | 36°F | 2.1" |
| March | 33°F | 58°F | 45°F | 3.2" |
| April | 43°F | 71°F | 56°F | 3.7" |
| May | 52°F | 78°F | 65°F | 5.6" |
| June | 61°F | 86°F | 74°F | 4.5" |
| July | 66°F | 90°F | 78°F | 4.2" |
| August | 65°F | 88°F | 76°F | 2.8" |
| September | 58°F | 82°F | 69°F | 3.5" |
| October | 46°F | 71°F | 58°F | 5.4" |
| November | 35°F | 59°F | 46°F | 2.6" |
| December | 29°F | 50°F | 39°F | 3.8" |
| Index | Herndon | Virginia | National |
| Air quality index | 47 | 58 | 42 |
| Pollution index | 380,124 | 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 | 0.003% |
| Benzene | 0.005% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.001% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Bull Run Mountain Estates, VA | 1,777 | 38 | 24.0% |
| Hamilton, VA | 708 | 38 | 24.0% |
| Woodburn, VA | 10,081 | 38 | 24.0% |
| Pimmit Hills, VA | 6,064 | 47 | 6.0% |
| Seven Corners, VA | 9,041 | 47 | 6.0% |
| Herndon, VA | 24,577 | 47 | 6.0% |
| City | Population | Air Quality Index | National Avg. |
| Pooler, GA | 24,575 | 39 | 22.0% |
| Palm River-Clair Mel, FL | 24,571 | 43 | 14.0% |
| Marysville, OH | 24,569 | 46 | 8.0% |
| Foothills No. 31, AB | 24,563 | n/a | |
| Norton Shores, MI | 24,557 | 38 | 24.0% |
| Herndon, VA | 24,577 | 47 | 6.0% |
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