Some of you may have noticed some interesting radar echoes displayed from the Springfield WSR-88D over the past several mornings. Circular patterns seem to appear right around the same time as a large pointed echo is displayed to the northeast of the radar site. What are causing these strange radar signatures?
The answer is... the sun and flocks of birds! This radar signature is common during the morning hours right around sunrise. The large spike emanating to the northeast occurs when the radar is pointed directly into the rising sun. The birds are best observed when cool air is trapped close to the Earth's surface. The cooler air causes the radar beam to bend to lower heights than normal. This allows objects like birds that are lower in the atmosphere to scatter energy back to the radar. The Ozarks have been under a relatively cool high pressure air mass for the last several days, making this an ideal situation for increased bending of the radar beam. The birds leave their nesting areas in the early morning and fly out in all directions. This is what causes the circular shape displayed on radar. Bodies of water are often collocated with the observed circular radar returns due to the fact that lakes and other bodies of water are often prime bird habitats.