WEATHER · CLIMATE NORMALS · 1991–2020
Philadelphia Climate — Averages by Month
What the weather in Philadelphia, USaverages across a standard 30-year period. Each month's figure is the 1991–2020 mean temperature and total rainfall from the ERA5 reanalysis — the long-run normal a place settles around, not a forecast for any particular day.
Month-by-month normals
| Month | Avg temperature | Avg rainfall |
|---|---|---|
| January | 0.9 °C · coldest | 84.9 mm |
| February | 2.1 °C | 77.9 mm |
| March | 6.3 °C | 106.4 mm · wettest |
| April | 12.3 °C | 94.4 mm |
| May | 17.7 °C | 92.3 mm |
| June | 22.8 °C | 100.9 mm |
| July | 25.4 °C · warmest | 101.1 mm |
| August | 24.3 °C | 98.3 mm |
| September | 20.5 °C | 106.4 mm |
| October | 14.1 °C | 92.7 mm |
| November | 8.3 °C | 75.4 mm |
| December | 3.5 °C | 102.8 mm |
How to read these numbers
These are reanalysis normals, not readings from a single weather station. They come from the ERA5 0.25° (~25 km) global reanalysis grid, sampled at the grid cell nearest Philadelphia — centred at 40.00°N, 75.25°W. A reanalysis blends observations with a physics model onto an even grid, so a coastal or mountain city's cell can read a little cooler, warmer, wetter or drier than the city centre itself. The month-to-month shape — when it's hot, when it rains — is what these normals capture best.
“Normal” means the 1991–2020 average, the current World Meteorological Organization standard period. A normal is what a place tends toward over decades — any single day, month or year can and will depart from it.