Two neat phenomena were detected this evening in quick succession by the WSR-88D at Vance AFB (KVNX). The first of these is a sunset echo, which was then quickly followed by bats taking flight out of their roosting site.
The sunset echo occured at 6:57 PM CDT (23:57 Z) and is indicated by the blue line segments extending west of the radar site. More on sunset echos can be found below.
The bats taking flight can be seen west/northwest of the radar site in Woods County, and is indicated by the expanding radar returns beginning at 7:06 PM CDT (00:06 Z) through 7:34 PM CDT (00:34 Z).
More on Sunset Echos
The WSR-88D radars can pick up the sun as an echo because the sun transmits radiation at all wavelengths. This includes the 10-cm long microwaves sent and received by the radars. When the sun is low in the sky, and a radar beam moves across it, the sun's 10-cm microwave emissions are strong enough to register in the radar receiver. Unfiltered, these echoes pass through the computer software processing and show up on radar displays. They are easily distinguished from precipitation echoes by their character: occurring only around sunrise or sunset, shaped straight, nearly uniform in intensity, elongated with the radar beam and facing the direction of the sun. (source: SPC)
It should be noted that the Twin Lakes WSR-88D in central Oklahoma also sampled a sunset echo on its 6:55 PM CDT scan.