Massive mayfly hatch picked up by radar in Wisconsin

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On the evening of July 20, 2014 mayflies hatched along the Mississippi river between Minnesota and Wisconsin in such great numbers that they were picked up by radar resembling light rain. The hatch began around 8:35pm. According to the National Weather Service: "this particular emergence was that of the larger black/brown Bilineata species. The radar loop below shows the reflected radar energy (reflectivity) from 8:35 pm to just after midnight. The higher the values (greens to yellows) indicate greater concentrations of flies. Note how the swarm is carried northward over time."

http://www.cbsnews.com/pictures/mayfly- ... wisconsin/