| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 26°F | 40°F | 33°F | 10.7" |
| February | 21°F | 34°F | 28°F | 2.7" |
| March | 31°F | 48°F | 40°F | 6.7" |
| April | 39°F | 59°F | 51°F | 4.2" |
| May | 48°F | 71°F | 62°F | 4.3" |
| June | 59°F | 80°F | 72°F | 7.9" |
| July | 63°F | 82°F | 74°F | 6.2" |
| August | 64°F | 82°F | 75°F | 13.8" |
| September | 56°F | 78°F | 69°F | 6.2" |
| October | 47°F | 66°F | 57°F | 6.5" |
| November | 35°F | 53°F | 44°F | 5.9" |
| December | 27°F | 38°F | 33°F | 2.9" |
| Index | Donegal | Pennsylvania | National |
| Air quality index | 36 | 45 | 42 |
| Pollution index | 7,262,690 | 4,584,805 | 2,726,193 |
| Measurement | Total |
| Days measured | 359 |
| Days with good air quality | 340 |
| Days with moderate air quality | 19 |
| 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. |
| Connellsville, PA | 7,414 | 36 | 28.0% |
| Vanderbilt, PA | 349 | 36 | 28.0% |
| Lemont Furnace, PA | 897 | 36 | 28.0% |
| Norvelt, PA | 862 | 36 | 28.0% |
| Rockwood, PA | 802 | 36 | 28.0% |
| Donegal, PA | 150 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Deering, AK | 150 | 38 | 24.0% |
| Nightmute, AK | 150 | 31 | 38.0% |
| Port Graham, AK | 150 | 31 | 38.0% |
| Garden City, IA | 150 | 37 | 26.0% |
| Palmer, IA | 150 | 37 | 26.0% |
| Donegal, PA | 150 | 36 | 28.0% |
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