Winter waterspouts (aka "snownados") are pretty uncommon, requiring a very specific set of meteorological conditions to form. Footage of the spiraling slush-columns is rarer, still (as in, there are six photos of them in existence) – a fact we like to think makes this snownado-video worth 90 seconds of your time.
The snowspout was spotted over the waters of western Lake Superior by Jordan Deters. He captured the above footage while overlooking the lake from near Knife River, Minnesota. Deters submitted the video and a number of questions to Minnesota Public Radio's chief meteorologist Paul Huttner, who was kind enough to reply in great detail on Updraft, MPR's meteorology blog (!). Here's an excerpt:
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.
More details over at Updraft.
Via Boing Boing