| 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 | Galena | Maryland | National |
| Air quality index | 42 | 43 | 42 |
| Pollution index | 2,654,190 | 5,342,367 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 293 |
| Days with moderate air quality | 72 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.002% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.004% |
| Lead | 0.000% |
| Mercury | 0.005% |
| City | Population | Air Quality Index | National Avg. |
| Smyrna, DE | 11,694 | 42 | 16.0% |
| Odessa, DE | 352 | 42 | 16.0% |
| Cecilton, MD | 901 | 42 | 16.0% |
| Sudlersville, MD | 423 | 42 | 16.0% |
| Hartly, DE | 167 | 42 | 16.0% |
| Galena, MD | 758 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Hartford, AR | 758 | 36 | 28.0% |
| Milner, GA | 758 | 38 | 24.0% |
| Plains, GA | 758 | 39 | 22.0% |
| Arco, ID | 758 | 27 | 46.0% |
| Boswell, IN | 758 | 42 | 16.0% |
| Galena, MD | 758 | 42 | 16.0% |
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