| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 21°F | 35°F | 27°F | 6.0" |
| February | 16°F | 30°F | 23°F | 2.8" |
| March | 26°F | 44°F | 34°F | 2.3" |
| April | 37°F | 56°F | 46°F | 5.0" |
| May | 46°F | 69°F | 57°F | 4.1" |
| June | 58°F | 79°F | 69°F | 5.2" |
| July | 61°F | 81°F | 70°F | 6.9" |
| August | 62°F | 80°F | 71°F | 9.1" |
| September | 55°F | 75°F | 65°F | 7.2" |
| October | 48°F | 64°F | 55°F | 3.9" |
| November | 33°F | 50°F | 41°F | 6.2" |
| December | 23°F | 34°F | 28°F | 3.1" |
| Index | Harmonsburg | Pennsylvania | National |
| Air quality index | 34 | 45 | 42 |
| Pollution index | 3,205,550 | 4,584,805 | 2,726,193 |
| Measurement | Total |
| Days measured | 358 |
| Days with good air quality | 334 |
| Days with moderate air quality | 23 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.170% |
| Mercury | 0.005% |
| City | Population | Air Quality Index | National Avg. |
| Cochranton, PA | 1,019 | 31 | 38.0% |
| Andover, OH | 549 | 34 | 32.0% |
| Conneaut Lake, PA | 674 | 34 | 32.0% |
| Pymatuning Central, PA | 2,253 | 34 | 32.0% |
| Springboro, PA | 309 | 34 | 32.0% |
| Harmonsburg, PA | 366 | 34 | 32.0% |
| City | Population | Air Quality Index | National Avg. |
| Gainesville, AL | 366 | 36 | 28.0% |
| Central, AZ | 366 | 47 | 6.0% |
| Clarksburg, CA | 366 | 52 | 4.0% |
| Gumbranch, GA | 366 | 39 | 22.0% |
| Calamus, IA | 366 | 46 | 8.0% |
| Harmonsburg, PA | 366 | 34 | 32.0% |
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