| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 25°F | 42°F | 33°F | 4.1" |
| February | 19°F | 39°F | 29°F | 3.3" |
| March | 27°F | 51°F | 38°F | 7.5" |
| April | 39°F | 62°F | 50°F | 7.2" |
| May | 46°F | 73°F | 60°F | 3.6" |
| June | 60°F | 84°F | 72°F | 4.8" |
| July | 62°F | 86°F | 74°F | 7.7" |
| August | 63°F | 86°F | 74°F | 8.7" |
| September | 54°F | 81°F | 67°F | 0.4" |
| October | 47°F | 71°F | 58°F | 10.0" |
| November | 33°F | 57°F | 45°F | 4.7" |
| December | 23°F | 41°F | 33°F | 4.8" |
| Index | Grantley | Pennsylvania | National |
| Air quality index | 41 | 45 | 42 |
| Pollution index | 12,532,500 | 4,584,805 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 299 |
| Days with moderate air quality | 66 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.180% |
| Benzene | 0.090% |
| Carbon Tetrachloride | 0.020% |
| Lead | 0.130% |
| Mercury | 0.270% |
| City | Population | Air Quality Index | National Avg. |
| Felton, PA | 644 | 41 | 18.0% |
| Jefferson, PA | 606 | 41 | 18.0% |
| New Freedom, PA | 4,691 | 41 | 18.0% |
| Seven Valleys, PA | 626 | 41 | 18.0% |
| Dallastown, PA | 3,889 | 41 | 18.0% |
| Grantley, PA | 4,320 | 41 | 18.0% |
| City | Population | Air Quality Index | National Avg. |
| Chester, MD | 4,319 | 46 | 8.0% |
| Cornwall, PA | 4,319 | 42 | 16.0% |
| Riva, MD | 4,321 | 47 | 6.0% |
| French Island, WI | 4,318 | 35 | 30.0% |
| Pixley, CA | 4,322 | 66 | 32.0% |
| Grantley, PA | 4,320 | 41 | 18.0% |
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