A forecast predicting life-threatening cold early next week has prompted the Rochester School District to make an announcement that classes next Monday have been canceled. The National Weather Service says wind chill readings Sunday night and Monday could be 40 to 50 below zero and the air temperature might only rise into the teens below zero Monday afternoon after dropping to between 20 and 25 below early Monday.  It could be the coldest blast of arctic air to visit the region since a record-setting cold snap in February of 1996.