| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 40°F | 30°F | 3.5" |
| February | 20°F | 42°F | 31°F | 3.1" |
| March | 28°F | 53°F | 40°F | 3.4" |
| April | 38°F | 67°F | 52°F | 3.9" |
| May | 48°F | 76°F | 62°F | 3.7" |
| June | 58°F | 84°F | 71°F | 5.5" |
| July | 63°F | 88°F | 75°F | 6.4" |
| August | 61°F | 85°F | 73°F | 5.0" |
| September | 54°F | 80°F | 66°F | 4.5" |
| October | 43°F | 68°F | 55°F | 5.4" |
| November | 33°F | 56°F | 44°F | 2.8" |
| December | 26°F | 45°F | 35°F | 4.9" |
| Index | Mertztown | Pennsylvania | National |
| Air quality index | 42 | 45 | 42 |
| Pollution index | 1,279,530 | 4,584,805 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 275 |
| Days with moderate air quality | 86 |
| 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. |
| Woxall, PA | 1,477 | 42 | 16.0% |
| Coplay, PA | 3,204 | 42 | 16.0% |
| Fullerton, PA | 15,415 | 42 | 16.0% |
| Stiles, PA | 1,195 | 42 | 16.0% |
| Lenhartsville, PA | 148 | 42 | 16.0% |
| Mertztown, PA | 933 | 42 | 16.0% |
| City | Population | Air Quality Index | National Avg. |
| Mi-Wuk Village, CA | 933 | 39 | 22.0% |
| Woods Hole, MA | 933 | 36 | 28.0% |
| Grawn, MI | 933 | 36 | 28.0% |
| Charlestown, NH | 933 | 34 | 32.0% |
| Salem, NY | 933 | 35 | 30.0% |
| Mertztown, PA | 933 | 42 | 16.0% |
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