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Strange radar images on Grand Rapids, Michigan Doppler radar

During the late evening hours on Tuesday, May 14, 2013 some strange images appeared on the Grand Rapids NWS Doppler radar. What were they?

Doppler radar is a valuable tool meteorologists use to track weather phenomena throughout the United States. Covering West Michigan, the National Weather Service (NWS) Doppler radar located near the G.R. Ford airport in Kentwood usually detects precipitation – like rain and snow, but sometimes it shows some rather ‘strange’ things, like Tuesday evening.

Starting around 11:15 pm it looked like a large thunderstorm was rapidly developing over southwest Mason County, south of Ludington. Doppler radar also indicated there might have been wind shear or rotation in that storm. The radar echo intrigued me when that ‘thunderstorm’ didn’t move – it remained stationary for 75-90 minutes. That’s when I remembered: wind turbines!

Consumers Energy’s newly-installed wind turbines went on-line in late November, 2012 but Doppler radar hasn’t ‘seen’ them until now, because it took a special set of weather circumstances Tuesday night.

Under normal conditions, any wavelength of energy – sunlight, radio waves, TV signals, radar beams, etc. travels in a straight line. Since the Earth is round, eventually these wavelengths can no longer be ‘seen’ beyond the horizon. That’s why you usually can’t see a boat five miles offshore in Lake Michigan or listen to a West Michigan radio station in Iowa.

So how could Doppler radar see wind turbines nearly 85 miles away with the height of the radar beam normally around 7000 feet? The answer: an ‘inversion’, defined as rapidly changing temperatures with height. This phenomenon caused the radar beam to bend – or refract downwards, following the curvature of the Earth then and reflect the radar signal off the moving wind turbines back to the radar.

I’m sure there will be other ‘strange’ radar images in the future, but trust your experienced local meteorologist- like me, to explain what you are seeing.