Meteorologists might insist that there is a pattern to the weather in Philadelphia, but to the rest of us, it's just random. It is not unheard of for the temperature to rise or fall 20 degrees in a matter of days as the seasons are changing. It's almost as if the local ecosystem is not quite sure which season comes next. However, if you are from the Northeast, the weather in Philadelphia will be nothing new. If you're from the South, expect much colder temperatures than you are used to in the winter; and if you hail from the West, get ready for some nice balmy humidity.
Basically, be ready for anything and everything. You will need an umbrella, good shoes for rain and snow, hats and gloves, a light jacket for fall, and a heavy jacket for winter. On the other hand, you also need bathing suits, shorts, and tank tops. If you are going home for fall break, bring your summer clothes home, and bring back winter clothes when you return. Then, at spring break, switch back. However, make sure that you always have something on hand for every kind of weather, as, now and then, the gods like to slip in a 30-degree day in April and a 70-degree day in January. Although you will experience the full seasonal spectrum here in Philly, the weather does tend to remain relatively mild all year round.