In my JW days I'd be inclined to blame this (and most anything else I couldn't explain) on demon activity. Nowadays watching the History channel's Unexplained, a disc-like object could be a candidate.
However, I received an email response from the National Weather Service. He says:
'That "ring" is produced by birds taking flight from overnight rest. This link will help...'
https://weather.com/science/weather-explainers/news/2018-11-08-radar-bird-ring-taking-flight
Frankly, some of your answers make a bit more sense.
Acluetofindtheuser had already found the NWS stock answer but he added "Your image seems to be too large for it to be birds".
I tend to agree, Aclue. Besides, a flying saucer is probably more appealing to the masses.