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Burst of Heavy Lake Effect Snow

Twin Ports, MN and WI

March 12 to 13, 2017

A Brief but highly efficient lake effect snow event occurred early in the morning on March 13, 2017. During the previous day, several bands of snow moved off the lake but were lighter and more transient so snow totals were held mostly in the one to two-inch range. The first radar loop from the National Weather Service in Duluth shown below shows light snow showers and a couple of very narrow, more organized bands affecting Duluth, MN, Superior, WI, and the surrounding region. The time of the loop was late afternoon March 12. During the nighttime, the snow area became more concentrated. After midnight the snow rapidly consolidated into a primary intense band producing snowfall rates of 2 to 3 inches per hour based on reports to the National Weather Service in Duluth. Snow accumulated 5 to 10 inches in Gary-New Duluth and in the city of Superior, with up to 13 inches in Morgan Park. The second radar loop shows the lake snow band dropping heavy snow. The band quickly weakened as it moved south of Superior after daybreak.

Radar images from the National Weather Service, Duluth, MN

The rapid intensification of the snow band may have been due to nighttime convergence that occurs over lakes due to differences in air temperature over the warm lake compared to colder air over land. If winds due to the large scale pressure pattern are light, then local scale influences will dominate the airflow. Cold dense air from land on both sides of the lake moves out over the lake to displace the warmer air and force it to rise. The enhanced lift from this process may have helped the snow band to intensify. The surface map shows light winds around 5 knots near the western tip of Lake Superior in the morning near daybreak.

Surface map 6 AM March 13, 2017 - National Weather Service Storm Prediction Center