| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 22°F | 38°F | 30°F | 3.2" |
| February | 23°F | 39°F | 30°F | 2.2" |
| March | 32°F | 52°F | 41°F | 3.4" |
| April | 43°F | 65°F | 53°F | 3.4" |
| May | 52°F | 74°F | 62°F | 4.2" |
| June | 60°F | 81°F | 70°F | 5.1" |
| July | 64°F | 84°F | 73°F | 5.1" |
| August | 63°F | 82°F | 72°F | 4.1" |
| September | 56°F | 77°F | 66°F | 3.1" |
| October | 46°F | 65°F | 54°F | 3.8" |
| November | 35°F | 54°F | 44°F | 2.8" |
| December | 28°F | 43°F | 35°F | 3.7" |
| Index | Irwin | Pennsylvania | National |
| Air quality index | 56 | 45 | 42 |
| Pollution index | 7,262,690 | 4,584,805 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 129 |
| Days with moderate air quality | 220 |
| Days w/ poor A.Q. for sensitive groups | 12 |
| Days with unhealthy air quality | 4 |
| 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. |
| Bear Rocks, PA | 1,174 | 36 | 28.0% |
| Norvelt, PA | 862 | 36 | 28.0% |
| Mount Pleasant, PA | 4,255 | 36 | 28.0% |
| Mammoth, PA | 428 | 36 | 28.0% |
| Calumet, PA | 1,415 | 36 | 28.0% |
| Irwin, PA | 3,773 | 56 | 12.0% |
| City | Population | Air Quality Index | National Avg. |
| Bright, NB | 3,772 | n/a | |
| Nellis AFB, NV | 3,770 | 54 | 8.0% |
| Larch Way, WA | 3,770 | 45 | 10.0% |
| Bayshore, NC | 3,776 | 34 | 32.0% |
| Mountain View, NC | 3,776 | 43 | 14.0% |
| Irwin, PA | 3,773 | 56 | 12.0% |
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