Weather in Philadelphia in January

The month to avoid. Of the twelve, January is the one to avoid. Highs sit at 3.7 °C and the day is short; this is an indoors-with-excursions month, not an outdoors-all-day one.

January ranks 12 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 9 days, 3 of them heavy. Enough to need a plan B, not enough to need a plan around it. Layers, and a genuinely waterproof outer — at 3.7 °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: 26 nights drop below freezing, so anything left outside stays frozen. Across the twenty years measured, the hottest January day reached 20.4 °C and the coldest night fell to -20.1 °C, and the wettest single day dropped 44 mm — roughly 56% of the month's rain in one day.

January is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest January on record still delivered 121 mm against 44 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 78 mm average is a reasonable planning figure, not a promise.

Wind is light at 8.1 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 84%, which at 3.7 °C means damp rather than muggy — the kind of cold that gets into a coat and stays there.

How January sits in the year

This is a turning point in the year — December and February sit on opposite sides of it, so the month contains the change rather than following it.

Daylight in January

January sits at the dark end of Philadelphia's year — 9.6 hours of daylight against 15 at midsummer, gaining 0.7 hours across the 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

Off season. The genuine off season: cheapest by a distance, with the caveat that some tours and restaurants close entirely.

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

January 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: January is a compromise. September is 57 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 January.