Walter Swiston, official observer for the FAA and the National Weather Service at O’Hare International Airport, shares this amazing winter mammatus cloud photo with us. Mammatus are best known to occur on the underside of thunderstorm anvils. But, the flood of milder air up and over the retreating arctic chill produced the clouds pictured above. Thanks Walter!
--By Tom Skilling, WGN-TV Chief Meteorologist
