According to the Weather Channel, there are only six known photographs of winter waterspouts in existence. Then, last week, Jordan Detters captured a good minute and a half of video, showing winter waterspouts dancing along the waves of Lake Superior near Knife River, Minnesota.
While water spouts are relatively common in warm months, producing one in the winter requires a pretty specific set of meteorological circumstances, writes Minnesota Public Radio's chief meteorologist Paul Huttner. Thus, the dearth of images. In fact, for one to form at all you need a temperature difference between the water and the air of 19 degrees C.
Winter waterspouts occur when meteorological conditions are just right. You need a bitter arctic air mass passing over relatively warm lake water, and just enough light, low level wind shear to get the rapidly rising air currents spinning nicely.
Saturday’s contrast between bitter arctic air (air temp was about -7 degrees at Two Harbors nearby) and relatively warmer lake water (offshore surface water temps were around 40 degrees) create an “enhanced lapse rate” as temps cooled rapidly with height above the water. That produces rising air, and the lift needed to generate strong updrafts. Slight wind shear gets the air spinning, and small vortexes can form into waterspouts over the lake.
Maggie Koerth-Baker is the science editor at BoingBoing.net. She writes a monthly column for The New York Times Magazine and is the author of Before the Lights Go Out, a book about electricity, infrastructure, and the future of energy. You can find Maggie on Twitter and Facebook.