Mayfly Hatch Shows Up on Radar in Minnesota

WINONA, Minn. - Shortly after 9 p.m. on Monday night, another massive mayfly hatch was spotted on the National Weather Service radar near La Crosse, Wisconsin. Mayflies were detected from near Winona, Minnesota south along the Mississippi River through Guttenberg, Iowa.

According to NWS, the radar detected the particularly large hatch with an "echo" above 20 dBZ reflectivity for the width of the river valley.

The weather service said the radar reflectivity values will increase for more dense concentrations of raindrops, birds or any airborne object -- in this case, the mayfly.

With time the mayflies will disperse, which can be seen with the lowering radar reflectivity values at the end of the radar loop (below).

NWS radar loop from 9 to 10 p.m. on July 19, 2010