Weather in Philadelphia in December

The month to avoid. December is the month most people should skip in Philadelphia. Highs sit at 6.8 °C and the day is short; this is an indoors-with-excursions month, not an outdoors-all-day one.

December ranks 10 of 12 — near the bottom of Philadelphia's year. September is the month that works, and the swing between the two is 57 points, which is a different holiday rather than a slightly better one.

Rain on 10 days, 4 of them heavy. Enough to need a plan B, not enough to need a plan around it. Layers, and a genuinely waterproof outer — at 6.8 °C the difference between a good day and a miserable one is entirely down to what you are wearing.

What the averages hide

Averages flatten a month, and this one hides a few things: 22 nights drop below freezing, so anything left outside stays frozen. Across the twenty years measured, the hottest December day reached 22.6 °C and the coldest night fell to -14.4 °C, and the wettest single day dropped 62 mm — roughly 56% of the month's rain in one day.

December is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest December on record still delivered 203 mm against 39 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 111 mm average is a reasonable planning figure, not a promise.

Wind is light at 7.2 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 85%, which at 6.8 °C means damp rather than muggy — the kind of cold that gets into a coat and stays there.

How December sits in the year

The month is on the way down: 6.1 °C cooler than November, with January dropping another 3.1 °C. The first week and the last are not the same trip.

Daylight in December

December sits at the dark end of Philadelphia's year — 9.4 hours of daylight against 15 at midsummer, holding steady all month. Sightseeing days are genuinely shorter, and an itinerary built for summer will not fit.

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

Quiet. Few other visitors, cheaper rooms, and a real chance some seasonal operators are shut.

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

December in Philadelphia versus nearby

If Philadelphia is one option among several, the nearby comparison is worth making. New York City is close enough to be a coin toss — within a degree on temperature, the same number of rain days. Washington is close enough to be a coin toss — within a degree on temperature, 1 day less rain.

So: December is a compromise. September is 48 points better and is what Philadelphia is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in Philadelphia

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