| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 24°F | 41°F | 31°F | 4.1" |
| February | 26°F | 44°F | 34°F | 5.6" |
| March | 34°F | 55°F | 43°F | 6.4" |
| April | 44°F | 68°F | 55°F | 6.1" |
| May | 55°F | 76°F | 64°F | 9.2" |
| June | 63°F | 84°F | 72°F | 6.0" |
| July | 66°F | 87°F | 76°F | 5.5" |
| August | 64°F | 85°F | 73°F | 7.7" |
| September | 58°F | 79°F | 67°F | 7.6" |
| October | 46°F | 67°F | 55°F | 9.4" |
| November | 36°F | 55°F | 44°F | 5.4" |
| December | 30°F | 46°F | 37°F | 6.8" |
| Index | Olney | Maryland | National |
| Air quality index | 47 | 43 | 42 |
| Pollution index | 15,133,000 | 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 | 0.130% |
| Carbon Tetrachloride | 0.060% |
| Lead | 0.070% |
| Mercury | 0.130% |
| City | Population | Air Quality Index | National Avg. |
| Monrovia, MD | 1,556 | 40 | 20.0% |
| Urbana, MD | 12,362 | 40 | 20.0% |
| Columbia, MD | 105,412 | 46 | 8.0% |
| Maryland City, MD | 17,681 | 46 | 8.0% |
| North Laurel, MD | 24,856 | 46 | 8.0% |
| Olney, MD | 35,350 | 47 | 6.0% |
| City | Population | Air Quality Index | National Avg. |
| Moose Jaw, SK | 35,355 | n/a | |
| La Porte, TX | 35,340 | 52 | 4.0% |
| Carrollwood, FL | 35,360 | 43 | 14.0% |
| Monroe, NC | 35,339 | 49 | 2.0% |
| Lufkin, TX | 35,336 | 36 | 28.0% |
| Olney, MD | 35,350 | 47 | 6.0% |
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