Gettysburg weather is not quite the same as DC weather, not quite the same as Baltimore weather, and not quite the same as Harrisburg weather, either. The campus is located in a unique setting in the Mid-Atlantic Chesapeake Bay Watershed. It can get very hot and humid in the summer and equally cold in the winter. Precipitation levels tend to be high year round.
Gettysburg is susceptible to heavy snowstorms and strong thunderstorms. It is in a valley, which means that it is almost always windy, which helps cool things off in the summer, but means that the wind chill is bitter in the winter. Of course, this doesn't preclude the possibility that it will remain 50 degrees and cloudy for weeks at a time-a state to which Gettysburg is prone, particularly in autumn and spring. Basically, all things considered, it is best to come to Gettysburg prepared for everything. Bring a raincoat, an umbrella, a winter coat, a light jacket, a wool hat, and sunglasses. You'll probably use them all.