| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 32°F | 44°F | 37°F | 2.7" |
| February | 32°F | 45°F | 38°F | 2.7" |
| March | 40°F | 55°F | 47°F | 3.4" |
| April | 51°F | 68°F | 59°F | 3.8" |
| May | 60°F | 76°F | 67°F | 3.9" |
| June | 70°F | 86°F | 77°F | 4.5" |
| July | 75°F | 90°F | 82°F | 5.0" |
| August | 73°F | 87°F | 79°F | 4.6" |
| September | 67°F | 80°F | 73°F | 4.4" |
| October | 55°F | 69°F | 62°F | 4.6" |
| November | 45°F | 58°F | 50°F | 2.4" |
| December | 37°F | 48°F | 42°F | 4.1" |
| Index | Garrison | Maryland | National |
| Air quality index | 46 | 43 | 42 |
| Pollution index | 3,089,800 | 5,342,367 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 223 |
| Days with moderate air quality | 129 |
| Days w/ poor A.Q. for sensitive groups | 13 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.003% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.070% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Westminster, MD | 18,649 | 42 | 16.0% |
| Brooklyn Park, MD | 15,163 | 46 | 8.0% |
| Jarrettsville, MD | 2,827 | 46 | 8.0% |
| Baltimore Highlands, MD | 7,880 | 46 | 8.0% |
| Ilchester, MD | 26,873 | 46 | 8.0% |
| Garrison, MD | 8,794 | 46 | 8.0% |
| City | Population | Air Quality Index | National Avg. |
| Live Oak, CA | 8,794 | 35 | 30.0% |
| Thief River Falls, MN | 8,792 | 33 | 34.0% |
| Clinton, MO | 8,792 | 47 | 6.0% |
| Glenshaw, PA | 8,791 | 56 | 12.0% |
| Nanaimo F, BC | 8,789 | n/a | |
| Garrison, MD | 8,794 | 46 | 8.0% |
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