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.

Winter Storm in EASTERN CLINTON, NEW YORK
From 12-JAN-18 20:00:00 to 13-JAN-18 10:00:00 (EST-5)
Property damage: 10.00K
Crop damage: 0.00K
Reported by: COOP Observer

Rain changed to a prolonged period of sleet Friday evening before changing to snow after midnight. Sleet accumulated around 1/2 to 1 inch with snowfall of 5 to 10 inches. A flash freeze made traveling nearly impossible through Saturday morning.

Winter Storm in NORTHERN FRANKLIN, NEW YORK
From 12-JAN-18 18:00:00 to 13-JAN-18 10:00:00 (EST-5)
Property damage: 10.00K
Crop damage: 0.00K
Reported by: COOP Observer

Rain changed to a prolonged period of sleet Friday evening before changing to snow after midnight. Sleet accumulated around 1/2 to 1 inch with snowfall of 8 to 15 inches. A flash freeze made traveling nearly impossible through Saturday morning.

Winter Storm in NORTHERN ST. LAWRENCE, NEW YORK
From 12-JAN-18 17:00:00 to 13-JAN-18 08:00:00 (EST-5)
Property damage: 10.00K
Crop damage: 0.00K
Reported by: COOP Observer

Rain changed to a prolonged period of sleet Friday evening before changing to snow just before midnight. Sleet accumulated around 1/2 with snowfall of 8 to 15 inches. A flash freeze made traveling nearly impossible through Saturday morning.

Winter Storm in SOUTHEASTERN ST. LAWRENCE, NEW YORK
From 12-JAN-18 17:00:00 to 13-JAN-18 08:00:00 (EST-5)
Property damage: 10.00K
Crop damage: 0.00K
Reported by: COOP Observer

Rain changed to a prolonged period of sleet Friday evening before changing to snow just before midnight. Sleet accumulated around 1/2 with snowfall of 8 to 15 inches. A flash freeze made traveling nearly impossible through Saturday morning.

Winter Storm in SOUTHWESTERN ST. LAWRENCE, NEW YORK
From 12-JAN-18 17:00:00 to 13-JAN-18 08:00:00 (EST-5)
Property damage: 10.00K
Crop damage: 0.00K
Reported by: COOP Observer

Rain changed to a prolonged period of sleet Friday evening before changing to snow just before midnight. Sleet accumulated around 1/2 with snowfall of 8 to 15 inches. A flash freeze made traveling nearly impossible through Saturday morning.

Flood in FRANKLIN, NEW YORK
From 12-JAN-18 20:00:00 to 13-JAN-18 23:00:00 (EST-5)
Location: HOGANSBURG
Flood cause: Ice Jam
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Several ice jams formed on the St. Regis River creating high water and areas flooding in the town of Hogansburg, NY. Numerous local roads were either flooded or threatened by high water, resulting in the evacuations of numerous homes.

Flood in FRANKLIN, NEW YORK
From 12-JAN-18 03:00:00 to 13-JAN-18 23:00:00 (EST-5)
Location: FT COVINGTON
Flood cause: Ice Jam
Property damage: 150.00K
Crop damage: 0.00K
Reported by: Emergency Manager

A large ice jam formed on the Salmon River in Fort Covington, NY and extended for several miles from the Route 37 bridge crossing north to near the international border. Up to 17 homes and 37 people were evacuated. Some damage to residences was reported.

Winter Storm in SOUTHERN FRANKLIN, NEW YORK
From 12-JAN-18 18:00:00 to 13-JAN-18 09:00:00 (EST-5)
Property damage: 10.00K
Crop damage: 0.00K
Reported by: COOP Observer

Rain changed to a prolonged period of sleet Friday evening before changing to snow just before midnight. Sleet accumulated around 1/2 with snowfall of 5 to 10 inches. A flash freeze made traveling nearly impossible through Saturday morning.

Winter Storm in WESTERN ESSEX, NEW YORK
From 12-JAN-18 19:00:00 to 13-JAN-18 10:00:00 (EST-5)
Property damage: 10.00K
Crop damage: 0.00K
Reported by: COOP Observer

Rain changed to a prolonged period of sleet Friday evening before changing to snow after midnight. Sleet accumulated around 1/2 with snowfall of 5 to 10 inches. A flash freeze made traveling nearly impossible through Saturday morning.

Winter Weather in EASTERN ESSEX, NEW YORK
From 12-JAN-18 21:00:00 to 13-JAN-18 10:00:00 (EST-5)
Property damage: 5.00K
Crop damage: 0.00K
Reported by: COOP Observer

Rain changed to a prolonged period of sleet Friday evening before changing to snow well after midnight. Sleet accumulated around 1/2 inch with snowfall of 2 to 5 inches. A flash freeze made traveling very hazardous.

Winter Storm in WESTERN CLINTON, NEW YORK
From 12-JAN-18 19:00:00 to 13-JAN-18 10:00:00 (EST-5)
Property damage: 10.00K
Crop damage: 0.00K
Reported by: COOP Observer

Rain changed to a prolonged period of sleet Friday evening before changing to snow after midnight. Sleet accumulated around 1/2 with snowfall of 6 to 12 inches. A flash freeze made traveling nearly impossible through Saturday morning.