| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 24°F | 40°F | 32°F | 2.5" |
| February | 24°F | 43°F | 33°F | 2.3" |
| March | 33°F | 53°F | 42°F | 2.7" |
| April | 43°F | 66°F | 54°F | 3.9" |
| May | 52°F | 75°F | 63°F | 3.9" |
| June | 62°F | 83°F | 73°F | 4.6" |
| July | 67°F | 87°F | 77°F | 4.4" |
| August | 64°F | 85°F | 74°F | 4.2" |
| September | 58°F | 79°F | 68°F | 3.4" |
| October | 47°F | 67°F | 56°F | 5.1" |
| November | 36°F | 55°F | 45°F | 2.4" |
| December | 29°F | 45°F | 36°F | 3.7" |
| Index | Duncannon | Pennsylvania | National |
| Air quality index | 44 | 45 | 42 |
| Pollution index | 11,091,200 | 4,584,805 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 252 |
| Days with moderate air quality | 107 |
| Days w/ poor A.Q. for sensitive groups | 5 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.140% |
| Carbon Tetrachloride | 0.030% |
| Lead | 0.310% |
| Mercury | 0.004% |
| City | Population | Air Quality Index | National Avg. |
| East Salem, PA | 132 | 44 | 12.0% |
| Berrysburg, PA | 295 | 44 | 12.0% |
| Harrisburg, PA | 49,247 | 44 | 12.0% |
| New Cumberland, PA | 7,305 | 44 | 12.0% |
| Paxtang, PA | 1,726 | 44 | 12.0% |
| Duncannon, PA | 1,305 | 44 | 12.0% |
| City | Population | Air Quality Index | National Avg. |
| Belfast, PA | 1,305 | 34 | 32.0% |
| Faxon, PA | 1,305 | 35 | 30.0% |
| Fraser, CO | 1,304 | 47 | 6.0% |
| Hastings, FL | 1,304 | 17 | 66.0% |
| Livonia, LA | 1,304 | 45 | 10.0% |
| Duncannon, PA | 1,305 | 44 | 12.0% |
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