The outbreak of arctic air across Minnesota on February 17, 2006 produced some interesting atmospheric phenomena for the citizens of Duluth. Steam devils were observed forming over the lake. Steam devils are produced by convective eddies of condensed water vapor that rise from a lake surface and swirl upward through the overlying cold air (having arisen from the warmer lake body). The wind will often initiate a rotation in the steam, giving it a fingerlike appearance, similar to a dust devil on land. An arctic air mass overlying open water and accompanied by strong wind speeds are essential ingredients.

Winds were blowing across Lake Superior at 30-40 mph on Friday, February 17th, with air temperatures only ranging from -7 to -11 degrees F. The Lake Superior surface temperatures were 33 to 36 degrees F, thus 40 F or more than the overlying air. Under such conditions the water vapor being released by the lake surface readily condenses into tiny droplets and rises through the cold air to great heights. Steam devils have been observed from aircraft to rise as high as 1500 ft. They are very ephemeral in nature lasting only seconds to a few minutes before they evaporate in the dry, arctic air. On occasion these steam devils are called arctic outbreak vortices, or frigid fog funnels. Photos of such atmospheric phenomena are rare because they are so infrequent.

Thanks goes out to University of Minnesota Climatologist and Meteorologist Mark Seeley for the description of this event.

View looking over Lake Superior from Duluth. Note the "lake effect" clouds forming as well. Photo credits: Richard Thomas and Dorothy Charging Hawk of the Duluth Reader/Weekly

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URL: http://climate.umn.edu/doc/journal/steam060217.htm
Last modified: February 24, 2006