| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 28°F | 47°F | 37°F | 2.7" |
| February | 29°F | 50°F | 38°F | 2.3" |
| March | 37°F | 60°F | 47°F | 3.2" |
| April | 47°F | 71°F | 58°F | 3.4" |
| May | 56°F | 78°F | 67°F | 4.6" |
| June | 67°F | 87°F | 77°F | 5.3" |
| July | 72°F | 91°F | 81°F | 4.2" |
| August | 70°F | 90°F | 79°F | 3.2" |
| September | 63°F | 83°F | 72°F | 3.5" |
| October | 52°F | 72°F | 61°F | 5.0" |
| November | 40°F | 61°F | 50°F | 2.5" |
| December | 33°F | 52°F | 42°F | 3.8" |
| Index | Forest Heights | Maryland | National |
| Air quality index | 47 | 43 | 42 |
| Pollution index | 2,776,590 | 5,342,367 | 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 | 0.070% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.020% |
| Mercury | 0.030% |
| City | Population | Air Quality Index | National Avg. |
| Franconia, VA | 19,478 | 47 | 6.0% |
| Idylwood, VA | 18,099 | 47 | 6.0% |
| Newington, VA | 13,452 | 47 | 6.0% |
| Rose Hill, VA | 21,846 | 47 | 6.0% |
| West Falls Church, VA | 31,262 | 47 | 6.0% |
| Forest Heights, MD | 2,739 | 47 | 6.0% |
| City | Population | Air Quality Index | National Avg. |
| Wolf Point, MT | 2,739 | 34 | 32.0% |
| South Congaree, SC | 2,739 | 43 | 14.0% |
| Arcadia, LA | 2,738 | 35 | 30.0% |
| Osseo, MN | 2,738 | 46 | 8.0% |
| Casselton, ND | 2,738 | 33 | 34.0% |
| Forest Heights, MD | 2,739 | 47 | 6.0% |
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