Doppler Radar Catches Car Going 130 MPH?

The NWS in Chicago posted a story yesterday that got picked up by Gizmodo, saying:

Here are some radar images from the time and area in question (courtesy Plymouth State); you can download larger versions of the entire radar scope here.

CLICK TO LOOP 10:30 PM - 1:30 AM C STORM-RELATIVE VELOCITY | SEE ALSO: VELOCITY | REFLECTIVITY

First, I have heard of birds, bats, buildings, wind turbines, and mountains showing up on Doppler (NEXRAD) radar before, but this was the first time I had heard of cars. That doesn't mean, however, that it didn't happen. Clearly the radar is picking up *something* along the interstates though I am not convinced it is cars. What else could it be? Signage, light poles, the road itself... I'm not sure. Given that it's picking up something around Dawson Lake, I'd bet on trees or poles before cars.

If it is cars, why did it misjudge that one was going 130 mph? First of all, I can't be sure that's the number, although the NWS scale goes farther than Plymouth State; the color (on the Plymouth State Storm-Relative Velocity radar) represents 50 (purple) to 122 (max readout) knots (58-140 mph), although that max of 122 could have been anywhere on the radar. The radar shows all kinds of random, outlandish velocities for non-meteorological objects - this is not big news (in fact to detect a mesocyclone or tornado, multiple pixels must be used). Weather radars aren't built to detect objects the size of a car; if they really could, they certainly couldn't tell one from another (another question, why is all the traffic going towards the radar (pink/purple) and none going away (blue/green)?