On Sunday night, the Doppler radar that serves the D.C.-Baltimore area detected a cloud that wasn’t made of raindrops.

The migrating birds were flying north after a long winter’s vacation around 9 p.m. on Sunday night. They were spotted on radar over northwest Charles County, heading northwest toward Fairfax County.

The KLWX radar saw migrating birds on Sunday evening, shown here in images from NWS Sterling’s Science and Operations Officer, Steve Zubrik. (Steve Zubrik via Facebook )

The birds were flying at approximately 45-50 mph, a speed that was determined using the velocity (Doppler) product on the radar images above. The Doppler component of radar measures the velocity of objects in the air — usually things like rain drops, snow or hail, but in this case birds.

Radars often pick up odd, non-precipitation echoes, including bats leaving their caves to feed in the evening, migrating monarch butterflies, and even waves of bugs along a frontal boundary.

Did you see the birds that evening?