Weather radar is picking up swarms of dragonflies from the Midwest to the Mid-Atlantic

Capital Weather Gang Analysis
Weather radar is picking up swarms of dragonflies from the Midwest to the Mid-Atlantic
When skies have been rain-free, radar is seeing big bugs.

By Matthew Cappucci, Meteorologist, Capital Weather Gang
September 13 at 4:12 PM

A glance at weather radar in the Midwest on Tuesday might have had you reaching for the umbrella. The only problem? It was a clear sunny day.

The likely culprit couldn’t have been rain. In fact, it probably wasn’t even meteorological. There’s a strong chance that these signatures came from dragonflies.

Social media video emerged showing swarms of dragonflies descending across the eastern third of the nation. From Ohio and Indiana to New Jersey, Maryland and Virginia, witnesses have reported the migrating dragonflies. And Doppler weather radar has likely detected the bugs as well.

This is not rain being observed by the radars across IN/OH/PA today. Care to take a guess as to what is traversing the region?

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Differential reflectivity reports data back as a number between negative-7.9 and +7.9. If an object is as tall as it is wide, it will reflect a zero signal. But for objects wider than they are tall, that number skews positive. Within the cloud of radar returns over Ohio Tuesday evening, differential reflectivity values ranged between positive 5 and 6. That means we’re likely talking something with a decent width compared to its height. Like, say, a swarm of dragonflies.



Differential reflectivity sees a lot of high values, plotted in pink. That represents a slurry of objects wider than they are tall. (NOAA/GR2 Analyst/Matthew Cappucci)

Robert LaPlante is the science and operations officer at the National Weather Service in Cleveland. He says there is a good chance that dragonflies contributed to the radar returns, but weren’t solely responsible. “Record high temperatures likely allowed them to fly higher,” he said. That makes it easier for radar to detect them.
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Matthew Cappucci is a meteorologist for Capital Weather Gang. He earned a B.A. in atmospheric sciences from Harvard University in 2019, and has contributed to The Washington Post since he was 18. He is an avid storm chaser and adventurer, and covers all types of weather, climate science, and astronomy. Follow https://twitter.com/MatthewCappucci