A very deep upper level trough from Central Canada to the Gulf of Mexico allowed for a warm, moist flow with temperatures in the 50s and 60s through midday on January 12th. By late afternoon, an arctic front moved into the St. Lawrence Valley, with temperatures plummeting into the 20s by evening and single digits by Saturday morning (1/13). In addition low pressure traveled along the front as it moved across Vermont delivering an inch or more of precipitation in the form of rain, freezing rain, sleet and snow.
Several impacts occurred with this event. First, temperatures 25 to 30 degrees above normal caused significant snow melt across the region and then an half inch or more of rainfall in January 12th both lead to some ice jams and localized flooding, especially along the Little Salmon in Fort Covington where dozens of residents were flooded and evacuated as well as the AuSable River in Essex county.
Second, rapidly falling temperatures accounted for rain changing to freezing rain, sleet then snow. Snow was more prevalent in the St. Lawrence Valley and northern Adirondacks with significant sleet in the Champlain Valley. Sharply falling temperatures allowed for a flash freeze of area roads making for extremely hazardous travel.
Third, the combination of earlier thawing and sub-zero temperatures allowed for freeze-up jams to develop with some major flooding in the Underwood trailer park along the Saranac River in Plattsburgh.