The general university policy is not to cancel classes for snow or other emergencies, but rather to hold all class meetings that can reasonably meet. The university has announcements pertaining to these issues made over Boston radio and television stations, or you can call the Snow/Info Line at 617-627-INFO for information.
In addition, Tufts will send out email notifications to all active Tufts email accounts regarding closures or emergencies, and those same notifications can be found at http://announcements.tufts.edu/