| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 23°F | 40°F | 31°F | 2.6" |
| February | 23°F | 42°F | 32°F | 2.4" |
| March | 31°F | 53°F | 41°F | 3.1" |
| April | 42°F | 66°F | 54°F | 3.6" |
| May | 51°F | 75°F | 63°F | 3.7" |
| June | 61°F | 84°F | 72°F | 4.8" |
| July | 66°F | 88°F | 77°F | 5.0" |
| August | 64°F | 85°F | 74°F | 4.7" |
| September | 57°F | 79°F | 68°F | 4.4" |
| October | 46°F | 67°F | 56°F | 4.8" |
| November | 35°F | 55°F | 45°F | 2.7" |
| December | 29°F | 45°F | 36°F | 3.8" |
| Index | St. Clair | Pennsylvania | National |
| Air quality index | 42 | 45 | 42 |
| Pollution index | 1,279,530 | 4,584,805 | 2,726,193 |
| Measurement | Total |
| Days measured | 360 |
| Days with good air quality | 278 |
| Days with moderate air quality | 78 |
| Days w/ poor A.Q. for sensitive groups | 4 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.002% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Nuremberg, PA | 445 | 38 | 24.0% |
| Altamont, PA | 534 | 42 | 16.0% |
| Frackville, PA | 3,753 | 42 | 16.0% |
| Lake Wynonah, PA | 2,762 | 42 | 16.0% |
| Minersville, PA | 4,278 | 42 | 16.0% |
| St. Clair, PA | 2,948 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Watonga, OK | 2,947 | 48 | 4.0% |
| New Hope, AL | 2,949 | 44 | 12.0% |
| Lido Beach, NY | 2,949 | 51 | 2.0% |
| Mountain View, AR | 2,946 | 36 | 28.0% |
| Gladwin, MI | 2,946 | 26 | 48.0% |
| St. Clair, PA | 2,948 | 42 | 16.0% |