Philadelphia's climate chart would make a hard mountain to climb with icy-cold winters at the start and end of the year and sweaty summers in the middle. Winds from the Atlantic Coastal Plain can be light cool breezes in summer or chilly gales in winter. Rainfall usually hovers around 76mm (3in) a year.
| Month | Temp (°C) | Rainfall (mm) | Humidity (%) | Sunshine (hours) |
| Jan | -3 - 4 | 84 | 5 | |
| Feb | -3 - 5 | 84 | 6 | |
| Mar | 1 - 9 | 86 | 7 | |
| Apr | 6 - 16 | 79 | 8 | |
| May | 12 - 22 | 84 | 8 | |
| Jun | 17 - 27 | 81 | 10 | |
| Jul | 20 - 29 | 104 | 10 | |
| Aug | 19 - 28 | 117 | 8 | |
| Sep | 16 - 24 | 79 | 8 | |
| Oct | 10 - 19 | 71 | 7 | |
| Nov | 4 - 12 | 69 | 5 | |
| Dec | -1 - 6 | 86 | 5 |