What Causes Lake-Effect Snow? (credit NWS, University of Michigan)

While the term "lake effect snow" may have little meaning for people who live a good distance away from the Great Lakes, people who live near the Great Lakes are very familiar with the extreme impacts it has on daily routines. The formation of lake effect snow first starts when cold air, that normally originates from Canada, drifts across the relatively warm waters of the Great Lakes.

​As the cold air travels across the lakes, warm moist air will begin rise into the lowest section of the atmosphere. This warm moist air will then cool and condense into lake effect clouds. These clouds will then congeal into these narrow bands of heavy snow or also known as "streamers" that could produce intense snowfall rates of  2 to 3 inches per hour. And depending on how cold the air is at the surface, the snowfall rates could be even higher. The graphic below is a brief description by the National Weather Service (NWS) showing how lake-effect snow forms. 

Wind direction plays a key role in not only the formation of lake-effect snow, but what areas receive the most snow from a lake-effect event. For example, after a low pressure system moves through the Great Lakes region, flow will be mostly dominate from the Northwest. Wherever that northwest flow is the strongest is where you will find lake-effect streamers with the most intense snowfall rates. Underneath these streamers, it may be snowing heavily or whiteout conditions could be present. And just a few miles down the road, the sun  could be shining with no snow accumulation on the ground. This goes to show how narrow a lake-effect streamer may be. Though streamers are very narrow, they could stretch for more than 100 miles from their original starting point. Sometimes, they could stretch as far east as the Appalachian mountains. 

Another key element that aid in the formation of lake-effect snow is the amount of instability or energy there is in the atmosphere. For lake-effect clouds to form, there needs to be a temperature difference of at least 13 degrees Celsius or 26 degrees Fahrenheit between the temperature of the lake and the temperature about 5,000 feet up in the atmosphere. This temperature difference provides the necessary ingredients for instability to build over the lakes which will allow the warm moist air to rise vertically. Sometimes, the amount of energy that forms from the instability could be enough to produce another fascinating and somewhat rare weather phenomenon called thundersnow. In other words, lightning that accompanies an intense snow band. And depending on your location, you may even be able to observe the actual lightning bolt. 

Other key factors for lake-effect snow include wind shear (change in wind speed and direction with height), fetch, the amount of moisture, synoptic forcing, and topography. But one factor that definitely takes a toll on the duration of lake-effect events is the percentage of ice cover over the lakes. As we head further into the winter season, the air will get colder and the lakes will gradually begin to freeze over.  The more ice there is covering the lakes, the chances for a lake-effect event become very slim. And the lake doesn't need to be completely frozen to stop the formation of lake-effect precipitation. That is why late fall and early winter is the time of the year where lake-effect events make there appearance the most. 

​One of the most known historical lake-effect events happened near Buffalo, NY just prior to Thanksgiving in 2014. This was a multi-day event that pummeled the Buffalo area with an astonishing 88 inches of lake-effect snow. Provided below are some of the mind-blowing snowfall totals and radar imagery by the NWS office in Buffalo from that multi-day event.  

- Cowlesville: 88 inches
- Orchard Park: 71 inches
- Lancaster: 74 inches
- Wales Center: 69.3 inches
- West Seneca: 52.5 inches
- Buffalo Int'l Airport: 16.9 inches
- Tonawanda: 7.9 inches

To learn more about other interesting and/or high-impact winter weather events occurring around the world, be sure to click here!

© 2018 Meteorologist Joseph Marino