That's not rain on Duluth's weather radar – it's birds

Meteorologists in Duluth were curious what the blue blob on radar was.
Publish date:
The blue blob on radar is indicative of birds, not rain. 

The blue blob on radar is indicative of birds, not rain. 

It's always fascinating when nature finds a way to light up a weather radar. It could be hundreds of thousands of bugs of bunches of birds, which was the case Tuesday morning along the North Shore of Lake Superior. 

The National Weather Service in Duluth noticed a blob of blue reflectivity on radar on the shoreline from Two Harbors to Duluth, but with clear skies and a rising sun there wasn't any precipitation falling. The radar had actually picked up on birds flying south, specifically seagulls and lake gulls. 

One would immediately imagine thousands of birds flying together to show up on radar as a large, blue blob. But that's not the case. 

"The bird density was about 3-6 birds at a time onscreen all going south," the weather service explained. "Radar returns are based on the diameter of the scatterer to the 6th power. So the birds look like large hail stones, they really light up the display even though there aren't as many as you'd think."

You can see them moving south on radar in this GIF from Jonathan Erdman

The Minnesota DNR says it's commonplace to see all kinds of gulls in Duluth and along North Shore year round. 

"The most easily-seen bird at Gooseberry, Herring Gulls are big, gray-backed gulls with pink legs. They nest on the cliff by the mouth of the river, and they are present year-round, but are not very common in winter. Sometimes other gulls stop here when they see the flock of Herring Gulls. Ring-billed Gulls, which nest in Duluth, sometimes visit here in summer. In winter, northern gulls, such as Glaucous Gulls, Thayer's Gulls, and Iceland Gulls sometimes make brief appearances. Great Black-backed Gulls show up on rare occasions, but their range is expanding from the east, so eventually they may be regular residents on the North Shore."

We featured a similar story involving geese flying over Aberdeen, South Dakota, in March 2018. And in July 2017, a massive mayfly hatch showed up on radar near La Crosse, Wisconsin. 

According to Smithsonian, birds and bugs were first seen on radar during World War II, and they're commonly seen now when birds take flight at night, then landing and resting before sunrise. 

That's appears to be exactly what happened this morning in Duluth. 

Next Up