MONTGOMERY, AL (WSFA) - So you're up bright and early, checking your WSFA Weather app on your phone. You pull up radar and notice an odd shaped doughnut of green around the Montgomery area. You look out the window and are surprised to see skies are sunny. Not a drop of rain. You refresh the app, but radar still shows the same thing. So what gives?
This morning's "rain ring" is actually something called a "roost ring". Believe it or not, a flock of birds leaving their roost for their morning breakfast is the culprit behind the radar echo. Remember, radar works by a beam of energy being reflected back to the radar site. Most time, that happens when rain/snow/ice are present, but other "non-meteorological" objects can do it to. Sometimes even bugs.
Thousands of birds taking flight simultaneously can be enough to be picked up by radar. This typically involves a circular ring spreading outward, often becoming less pronounced as the birds travel farther from their roosting site. It's a simple concept...5,000 birds over ten square miles will be much easier for radar to pick up then those same 5,000 birds spread over 50 square miles. Eventually, the ring on radar fades away and the birds get their breakfast.
Pay attention just before sunrise each morning. You'll sometimes see these roost rings pop up in various areas, often in the same spot where the birds fly back during the evening only to take off again the next morning.