Weather in Philadelphia in May

A good month. May is a solid month to be in Philadelphia. Highs average 22.3 °C, lows 10.9 °C, and rain falls on 12 days — nothing in the month is working against you.

May ranks 3 of 12 in Philadelphia. Only September scores clearly higher, and the difference is small enough to be settled by price rather than weather.

Rain on 12 days, 3 of them heavy. Enough to need a plan B, not enough to need a plan around it. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

The averages here are honest — no hidden extremes worth planning around. Across the twenty years measured, the hottest May day reached 31.8 °C and the coldest night fell to 0.4 °C, and the wettest single day dropped 37 mm — roughly 39% of the month's rain in one day.

May is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest May on record still delivered 168 mm against 35 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 96 mm average is a reasonable planning figure, not a promise.

Wind is light at 6.7 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 79%, high enough to notice on the warm days without dominating them.

How May sits in the year

The month is on the way up: 5.2 °C warmer than April, and June adds another 4.6 °C. Late in the month feels noticeably different from the start of it, which is worth knowing if the trip is short.

Daylight in May

May is at or near the longest days of Philadelphia's year: 14.4 hours of daylight, gaining 0.9 hours across the month. Evenings are the real gain — dinner outdoors still happens in full light.

An inland climate

With no coast nearby, the year swings a fair way — 34.9 °C between the warmest afternoons and the coldest nights, wider than any coastal city at this latitude would manage.

How busy it gets

Peak season. Expect the highest prices of the year and to be booking well ahead.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

May in Philadelphia versus nearby

If Philadelphia is one option among several, the nearby comparison is worth making. New York City is the weaker option in May — 5.3 °C cooler, 1 day more rain. Washington is close enough to be a coin toss — within a degree on temperature, 1 day more rain.

So: May is effectively as good as it gets here — 4 points behind September, which is inside the margin where the weather stops being the deciding factor and price starts being it.

Every month in Philadelphia

See all twelve months in Philadelphia, or where else to go in May.