Weather in Philadelphia

July is the warmest month (average 24.5°C, high 29.7°C) and January is the coolest (average -0.8°C, low -5.1°C). That 25.3°C swing in monthly averages is the first thing to plan around in Philadelphia.

Rain is rain in every month and about 1226 mm across the year. The wettest month is July at 124 mm; the driest is January at 78 mm. Philadelphia is in United States at 40.0°N. The 2001–2020 NASA POWER daily record describes a continental climate with a wide temperature swing. On this site the months that score closest to a 22°C day, lighter rain, and moderate humidity are June, August, and September.

Best months to visit Philadelphia

The three months with the highest comfort score are June, August, and September: June (21.4°C average, 121 mm, 79% humidity); August (24.1°C average, 121 mm, 74% humidity); September (20.6°C average, 102 mm, 74% humidity). They fall in calendar order. The score rewards averages near 22°C, lower rainfall, and humidity near 60%. It is a climate score, not a festival or price calendar.

If you prefer the hottest stretch, that is July. The coolest stretch is January.

How warm Philadelphia gets

Philadelphia has a 25.3°C gap between its coolest monthly average (-0.8°C in January) and its warmest (24.5°C in July). That is a northern-hemisphere pattern.

Mean high across all twelve months is 17.3°C and mean low is 6.9°C. These are 20-year grid averages, so a city station can read a few degrees warmer or cooler.

When Philadelphia gets wet

Rain does not take a season off. Philadelphia receives about 1226 mm a year, and even January still sees 78 mm. July is the peak at 124 mm and 14 days with at least 1 mm.

A rainy day here is a day with at least 1 mm in the NASA POWER series. July averages 14 such days; January averages 9.

The calendar in Philadelphia

The year bottoms out in January. Plan for -5.1°C at night and 3.4°C in the afternoon. February: 5.1°C high, -4.4°C low, 78 mm rain, 83% humidity. In March, Philadelphia averages 10.0°C by day and -0.8°C at night, with 100 mm of rain. April brings 97 mm and 11 rainy days; temperatures run from 4.8°C to 16.9°C. May stands apart from the months beside it: 22.0°C / 10.7°C and 96 mm. June: 26.7°C high, 16.1°C low, 121 mm rain, 79% humidity.

July is both the hottest and wettest month: highs around 29.7°C, 124 mm of rain, and 75% humidity. August brings 121 mm and 13 rainy days; temperatures run from 18.8°C to 29.4°C. September stands apart from the months beside it: 26.3°C / 14.9°C and 102 mm. October stands apart from the months beside it: 19.3°C / 8.4°C and 110 mm. November brings 90 mm and 8 rainy days; temperatures run from 2.3°C to 12.7°C. In December, Philadelphia averages 6.6°C by day and -2.0°C at night, with 111 mm of rain.

How Philadelphia compares inside United States

New York City is about 130 km away: Philadelphia is 0.8°C warmer than New York City in its hottest month and 87 mm drier over the year than New York City. New York City’s wettest month is December (133 mm) versus July here.

Manhattan is about 137 km away: Philadelphia is 0.5°C warmer than Manhattan in its hottest month and a similar annual rainfall (1236 mm in Manhattan). Manhattan’s wettest month is October (122 mm) versus July here.

Chicago is about 1069 km away: Philadelphia is 1.9°C warmer than Chicago in its hottest month and 244 mm wetter over the year than Chicago. Chicago’s wettest month is May (117 mm) versus July here.