Nature Note: The Lake Champlain Snow Globe

While the sun shines in Montpelier, snow could be dumping from the clouds 50 miles southwest in Cornwall, VT. Apart from major snowstorms—namely Nor’easters—the formation of lake-effect snow over Lake Champlain is one of the weather patterns that turns the Champlain Valley into a winter wonderland. Lake-effect snows requires a big lake. This weather phenomenon is also common on the Great Lakes and New York’s Finger Lakes. Whether the snow makes you jump for joy or want to escape to warmer realms, it’s a staple of the winter experience in the Champlain watershed.

Three conditions prime the pump for lake-effect snow. First, a mass of cold air, usually from Canada, must move over a body of comparatively warmer water. Second, the difference in temperature between the air of the upper atmosphere (between 2,000 and 16,000 feet) and the water must be high (59 degrees Fahrenheit is an approximate minimum temperature difference). Third, the cold air mass and the warm water mass must stay in contact with one another long enough for the air to absorb warmth and moisture.

On Lake Champlain, wind direction and lake width are limiting factors for lake-effect snows. Since Lake Champlain is 120 miles long and oriented north-south, only northerly winds stay in contact with the lake long enough to generate lake-effect snow. The lake’s greatest east-west distance, 12 miles between Port Kent, NY and Burlington, VT, is too narrow for this weather phenomenon to generate snow. Lake-effect snow is most likely to occur in Addison County, VT, where wind blowing from the Richelieu River hits land near Otter Creek.

Lake-effect snow is typically most intense near the shore. As warm moist air comes over land, it slows down because the land has greater friction than the water surface. Wind continues to hit the land and has nowhere to go but up. The air rises to the cooler upper atmosphere. As the water in the air cools, it condenses, forming snow. Lake-effect snow bands typically produce two to three inches of snow per hour.

The Champlain Valley experienced strong lake-effect snow showers a few times this season, with the last one dumping more than six inches in lakeside regions during December 20-21, 2024.