Photo: Satellite image of Lake-Effect Snow over the Great Lakes region on January 5, 2015. (Image courtesy of The Weather channel)
Lake-effect snow primarily affects the Great Lakes region of the Midwestern United States but can have an impact on any region near a lake, capable of the ideal temperature differential to form these snows. The difference of 13 degrees Celsius in lake water temperature and air one mile above the surface is the ideal and primary ingredient necessary to form lake-effect snow. While there are other bodies of water that can have this effect (rivers, oceans, etc.), the focus of this discussion will be on lakes. The intensity of these storms can create snowfall rates of 2-3 inches in an hour and have liquid rain to snow equivalent (in inches) ratios anywhere from 1:15 to 1:30. Due to stronger updrafts (faster rising air) from the temperature differential over the lake, this leads to a higher ratio, higher snowfall rates and greater impacts to travel.
The Great Lakes is the most common region where this phenomenon occurs, impacting the surrounding coasts based on the wind direction steering the snow bands. Typical lake-effect snow events are steered by a variety of north winds that brings in cold air needed to generate this phenomenon. Other locations with bodies can experience lake-effect snow like the Great Salt Lake in Utah and the finger lakes in New York. Regions can also experience ocean, river or sea-effect snow if the conditions are right.
There are multiple types of lake-effect snow bands that can occur based on wind direction and can have various impacts. Short lake axis parallel (SLAP) bands are often multiple small bands that follow the short axis of the lake and impact multiple smaller areas. Long lake axis parallel bands are often single bands following the long axis, usually creating a larger band with impacts over a single greater area. Other types of lake-effect snow are those that make multiple lake interaction, form and remain mainly over the lake, and form a vortex (or a small scale low pressure system, often called a meso-low) that can bring snows onshore. Due to shifting wind directions and weak synoptic (large scale) winds, vorticies can form within the snow band or over the lake. If stronger winds were present, a vortex will generally break up, but with cold air present and weak wind directional changes they can form and bring snow inland.
Photo: Map of Lake Michigan with red line indicating the Short Axis of the lake and the black line indicating the long axis of the lake. Image courtesy of the University of Michigan.
Terminology can often be confused when discussing lake induced snow events and how they impact a region. Since there is a difference between lake-effect and lake-enhanced snows, the distinction is necessary to discuss. Lake-effect produces snowfall as an effect of the presence of the lake, thus if the lake were not present, then the temperature differential needed to form the band would not exist. On the other hand, lake enhancement will enhance the snow production of a lake-passing system because of cold air aiding the development of clouds while passing over the warmer waters.
Understanding the nature of different types of lake-effect snow will help determine the impacts to a specific region based on the size of the bands. Forecasting is difficult for lake-effect snow because of the mesoscale nature of the event, but there are multiple processes that we can use to better that prediction. Nowcasting becomes necessary to concentrate on the changing structure of the bands and pinpoint the direct impacts to a town. Overall, lake-based snow systems are location dependent on proximity to a lake and how far inland these systems can impact. The best practice during winter storms would be to be aware of and prepared for rapidly changing conditions in real-time to determine the impacts to your specific location.
To learn more about other interesting winter weather topics from around the world, click here!
© 2018 Meteorologist Jason Maska