Props to Unhindered by Talent and Pharyngula for bringing this to my attention.
Large Mayfly Hatch Caught on Radar Friday June 30th
A large mayfly hatch occurred along the Mississippi River Friday evening, June 30th. The hatch began just after sundown, around 9 PM, and continued through the early morning hours. Those with plans outdoors Friday evening on and along the Mississippi River certainly noticed the huge swarm of mayflies, and their attraction to light. Some roads across the Mississippi River in and around La Crosse were covered with bugs, piling into "drifts" on bridges over the Mississippi River and its tributaries. Local businesses with high intensity lighting soon found large piles of dead mayflies accumulating under the lights by midnight. Below is a radar loop from the National Weather Service’s WSR-88D Doppler Radar in La Crosse. Notice the rapid increase in radar echoes along the Mississippi River channel...occurring simultaneously the entire length of the channel. The ambient wind flow was from the south on Friday evening, with the entire swarm of mayflies drifting north with time. The radar loop starts just before 9 PM CDT and ends around 1030 PM CDT.
This is very cool. Be sure to follow the link to the NOAA site to view the animated GIF of this.