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Its New England, What Do You Expect?
College Tours usually happen in the Spring or Fall because that's when campus looks its best ( and the campus is beautiful). Those are the two best seasons in New England.
The winter is very cold, with lots of snow ( usually) but since most students live on campus, or conveniently close to campus ( if they live off campus), then BC rarely shuts down due to snow storms.
However, the maintenance staff usually do a good job of cleaning snow and ice to make it safe for students and staff. Just wear lots of layers.