| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 22°F | 35°F | 28°F | 0.6" |
| February | 22°F | 36°F | 28°F | 0.4" |
| March | 30°F | 49°F | 39°F | 0.4" |
| April | 41°F | 62°F | 51°F | 0.4" |
| May | 50°F | 71°F | 60°F | 0.5" |
| June | 58°F | 78°F | 68°F | 0.9" |
| July | 62°F | 82°F | 72°F | 0.6" |
| August | 60°F | 80°F | 69°F | 6.0" |
| September | 54°F | 73°F | 63°F | 0.7" |
| October | 44°F | 62°F | 53°F | 0.9" |
| November | 34°F | 50°F | 42°F | 0.8" |
| December | 27°F | 40°F | 33°F | 0.6" |
| Index | Mifflin | Pennsylvania | National |
| Air quality index | 44 | 45 | 42 |
| Pollution index | 1,656,460 | 4,584,805 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 267 |
| Days with moderate air quality | 98 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.005% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.004% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Beavertown, PA | 1,080 | 35 | 30.0% |
| East Waterford, PA | 174 | 36 | 28.0% |
| East Salem, PA | 132 | 44 | 12.0% |
| Mifflintown, PA | 954 | 44 | 12.0% |
| Barrville, PA | 182 | 44 | 12.0% |
| Mifflin, PA | 381 | 44 | 12.0% |
| City | Population | Air Quality Index | National Avg. |
| Louviers, CO | 381 | 58 | 16.0% |
| Donahue, IA | 381 | 46 | 8.0% |
| Liscomb, IA | 381 | 37 | 26.0% |
| Mesick, MI | 381 | 36 | 28.0% |
| Wood Lake, MN | 381 | 32 | 36.0% |
| Mifflin, PA | 381 | 44 | 12.0% |
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