When the movie was filmed in the winter of 1993-1994, there was already at least a meter of snow on the ground in Harvard Square and in all of Boston. However, because the actual snow did not look "real" enough to be filmed, it was all cleared away and replaced with artificial snow.
The graduation scenes were filmed at University of Illinois Urbana-Champaign. The large building in front of the graduates is Foellinger Auditorium, made up to look like a Harvard building. Many of the graduates are UIUC students.