Lake effect snow! Why does it happen?

Grab a hot cup of coffee, this edition highlights the “lake effect snow” phenomenon! Lake effect snow is another fantastic example of how overlapping variables in the environment come together at the right time to generate significant weather.

As the name implies, for lake effect snow to happen at all it begins with the presence of the Great Lakes. Importantly, the large scale and water depth of the collective lakes in that region are a major source of stored heat energy due to water’s tremendously high specific heat capacity compared to other substances, such as air and land. Consequently, vast water bodies, including large lakes, tend to “remember”, so to speak, the previous season’s temperatures longer than the surrounding land and any transient air masses passing by, as well.

For the Great Lakes region, the transition between autumn and winter marks a time when the land and air are much more representative of expected colder seasonal temperatures versus the relative warmth provided by the lakes. As the lakes are still in the middle of what could be called a “temperature hangover” from late summer and early fall, there becomes a notable heating imbalance in the local environment between the warm surface of the lakes and frigid passing air masses overhead.

To elaborate on the temperature contrast a bit, lakes may be in the upper 40s and low 50s Fahrenheit early winter, while air moving above a few thousand feet up could be in the teens or colder. We are talking a 30 to 40 degree difference over a pretty short altitude climb. That is ridiculous! The positive buoyancy (rising air motion) greatly destabilizes the lower atmosphere, while plentiful evaporation from the warmer lakes continually feed water vapor to condense into deep clouds and ultimately freeze to generate snowfall and, yes, thundersnow!

Adding to atmospheric lift to help precipitation formation are lines of low-level convergence as wind over land encountering more friction tends to bend towards and collide with air moving across lakes. These wind convergence lines often serve as localized focal points for heavy, continuous snowfall, hence the term “snow bands”.

Photo Credit: Jonny William Malloy