Lake effect snow is a localized storm phenomena that results from a combination of variables.

When the lakes are not completely frozen over and the temperature of the lake is warmer than the temperature of the air, conditions are present that allows the air to increase the water vapor content. Air holds a certain amount of moisture dependent on its temperature. The amount of moisture in the air compared to the amount the air can hold is called relative humidity.

As wind currents move west to east (across the lake) and cold air moves down from Canada over the lakes, the air picks up moisture from the warmer lake and deposits it on the eastern or southeastern side (downwind) of the lake. This results in lake effect snow.

An increased rate of warming in the northern Great Lakes allow for more moisture to be absorbed. This may result in larger lake effect snow events to the east of a lake (see image).