Huge 'Mayfly Hatch' Caught On Radar, Overwhelms Upper Midwest

On the evening of July 20, 2014 mayflies hatched along along the Mississippi river between Minnesota and Wisconsin in such great numbers that they were picked up by radar resembling light rain.

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 .... http://www.cbsnews.com