| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 27°F | 41°F | 35°F | 2.2" |
| February | 28°F | 45°F | 37°F | 1.4" |
| March | 36°F | 54°F | 45°F | 4.8" |
| April | 46°F | 65°F | 56°F | 1.6" |
| May | 55°F | 73°F | 65°F | 8.1" |
| June | 64°F | 82°F | 75°F | 3.0" |
| July | 70°F | 87°F | 80°F | 0.5" |
| August | 67°F | 84°F | 76°F | 1.1" |
| September | 61°F | 78°F | 70°F | 1.7" |
| October | 50°F | 68°F | 59°F | 7.1" |
| November | 39°F | 57°F | 48°F | 2.9" |
| December | 33°F | 47°F | 40°F | 4.4" |
| Index | Jarrettsville | Maryland | National |
| Air quality index | 46 | 43 | 42 |
| Pollution index | 9,823,920 | 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 | 0.010% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.050% |
| Lead | 0.030% |
| Mercury | 0.140% |
| City | Population | Air Quality Index | National Avg. |
| New Freedom, PA | 4,691 | 41 | 18.0% |
| Railroad, PA | 321 | 41 | 18.0% |
| Fawn Grove, PA | 462 | 41 | 18.0% |
| Shrewsbury, PA | 3,842 | 41 | 18.0% |
| Glen Rock, PA | 2,332 | 41 | 18.0% |
| Jarrettsville, MD | 2,827 | 46 | 8.0% |
| City | Population | Air Quality Index | National Avg. |
| Holualoa, HI | 2,827 | 16 | 68.0% |
| Kings Beach, CA | 2,826 | 44 | 12.0% |
| Granville, WV | 2,828 | 36 | 28.0% |
| Villano Beach, FL | 2,829 | 31 | 38.0% |
| Sheridan, IL | 2,829 | 0 | 100.0% |
| Jarrettsville, MD | 2,827 | 46 | 8.0% |
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