| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 24°F | 43°F | 33°F | 2.3" |
| February | 25°F | 45°F | 34°F | 1.7" |
| March | 33°F | 56°F | 43°F | 2.9" |
| April | 42°F | 68°F | 55°F | 3.7" |
| May | 51°F | 76°F | 63°F | 4.5" |
| June | 60°F | 84°F | 72°F | 3.9" |
| July | 64°F | 88°F | 76°F | 3.3" |
| August | 62°F | 86°F | 74°F | 3.1" |
| September | 56°F | 80°F | 67°F | 3.3" |
| October | 45°F | 68°F | 56°F | 4.2" |
| November | 35°F | 57°F | 45°F | 2.4" |
| December | 28°F | 47°F | 37°F | 3.2" |
| Index | Ernstville | Maryland | National |
| Air quality index | 40 | 43 | 42 |
| Pollution index | 16,230,700 | 5,342,367 | 2,726,193 |
| Measurement | Total |
| Days measured | 362 |
| Days with good air quality | 306 |
| Days with moderate air quality | 54 |
| Days w/ poor A.Q. for sensitive groups | 2 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.130% |
| Carbon Tetrachloride | 0.090% |
| Lead | 0.080% |
| Mercury | 0.020% |
| City | Population | Air Quality Index | National Avg. |
| Mercersburg, PA | 1,673 | 36 | 28.0% |
| Needmore, PA | 92 | 36 | 28.0% |
| Big Pool, MD | 85 | 40 | 20.0% |
| Fairview, MD | 16 | 40 | 20.0% |
| Pinesburg, MD | 255 | 40 | 20.0% |
| Ernstville, MD | 25 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Mendeltna, AK | 25 | 31 | 38.0% |
| Beyerville, AZ | 25 | 31 | 38.0% |
| Butte Meadows, CA | 25 | 46 | 8.0% |
| Lazy Lake, FL | 25 | 41 | 18.0% |
| Blanchard, IA | 25 | 43 | 14.0% |
| Ernstville, MD | 25 | 40 | 20.0% |
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