* WHAT...Heavy snow expected. Total snow accumulations of 8 to 12 inches in the Wyoming Valley with snowfall amounts of 12 to 18 inches across the northern Tier of PA and central New York. Localized amounts up to two feet possible in the Southern Tier of NY and northern Tier of PA eastward toward the Catskills. Snow may mix with or change to sleet for a time in the Wyoming Valley. * WHERE...Portions of central New York and northeast Pennsylvania. * WHEN...From 1 AM Sunday to 7 PM EST Monday. * IMPACTS...Travel could be very difficult to impossible. The hazardous conditions can impact travel on Sunday along with the Monday morning and evening commutes. * ADDITIONAL DETAILS...Snow will overspread Northeast PA and the New York Southern Tier around daybreak Sunday morning, moving north to the I-90 corridor by the mid-morning hours on Sunday. At this time, the heaviest snowfall is forecast to be from south-central NY and areas along the NY/PA line. However, further adjustments to the storm track are possible. Snowfall could be very heavy at times Sunday afternoon into Sunday night with hourly rates exceeding 2 inches per hour.