* WHAT...Heavy snow expected. Total snow accumulations 12 to 18 inches. * WHERE...Monroe, Wayne, Northern Cayuga, Oswego, Jefferson, and Lewis Counties. * WHEN...From 7 AM Sunday to 7 AM EST Tuesday. * IMPACTS...Travel will be very difficult. The hazardous conditions will impact the Monday morning and evening commutes. * ADDITIONAL DETAILS...The bulk of the heavy snow is expected Sunday afternoon through Sunday night, with heavy snow continuing along the southern shore of Lake Ontario to Oswego county through Monday night.