| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 24°F | 38°F | 31°F | 4.7" |
| February | 23°F | 39°F | 31°F | 4.1" |
| March | 33°F | 51°F | 42°F | 6.1" |
| April | 42°F | 63°F | 54°F | 4.9" |
| May | 52°F | 72°F | 63°F | 6.5" |
| June | 60°F | 78°F | 70°F | 7.0" |
| July | 64°F | 82°F | 74°F | 9.5" |
| August | 62°F | 80°F | 72°F | 7.4" |
| September | 56°F | 74°F | 66°F | 6.3" |
| October | 45°F | 63°F | 55°F | 5.9" |
| November | 35°F | 52°F | 44°F | 5.6" |
| December | 29°F | 43°F | 36°F | 6.4" |
| Index | Derry | Pennsylvania | National |
| Air quality index | 39 | 45 | 42 |
| Pollution index | 7,262,690 | 4,584,805 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 296 |
| Days with moderate air quality | 69 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.030% |
| Benzene | 0.090% |
| Carbon Tetrachloride | 0.260% |
| Lead | 0.140% |
| Mercury | 0.030% |
| City | Population | Air Quality Index | National Avg. |
| Mammoth, PA | 428 | 36 | 28.0% |
| Jennerstown, PA | 1,172 | 36 | 28.0% |
| Bear Rocks, PA | 1,174 | 36 | 28.0% |
| Norvelt, PA | 862 | 36 | 28.0% |
| Mount Pleasant, PA | 4,255 | 36 | 28.0% |
| Derry, PA | 2,317 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| Victor, ID | 2,317 | 43 | 14.0% |
| Phillipsburg, KS | 2,317 | 19 | 62.0% |
| Lake Ozark, MO | 2,317 | 39 | 22.0% |
| Blue Mound, TX | 2,317 | 51 | 2.0% |
| Pine Crest, TN | 2,318 | 45 | 10.0% |
| Derry, PA | 2,317 | 39 | 22.0% |
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