STORM2K

Looking at KDMX (Des Moines) tonight, I noticed this strange AP (that's analagous(?) precipitation, I think - stuff that isn't supposed to be there ) forming out of the radar to the east at the same angle off of north as the sunset was to the west. The only difference was that the sunset beam was in the 01:47Z and 01:52Z scans and strongest in the first one, and the other beam started forming in the 01:42Z scan and got stronger through the 01:57Z scan, and was last visible on the 02:01Z scan. Anyway, I hadn't seen this before and I was wondering if anyone had any idea as to the reason behind this occurance?

Weather radars are capable of picking up radio noise from the Sun and in fact, the AWS used to boresight the FPS-77 radars using the Sun. In radio waves the Sun is larger than in visible light by about a factor of 3.

Steve

OK, so that's the one on the left hand side (labeled sunset), but what's the one on the right is my question.

Wind runner, The only other conceivable radar that I was able to see within the line of sight along the radial on the right was the Green Bay, WI radar. Weather radars that are in the vicinity of one another are calibrated to transmit along slight different frequencies in order to minimize interference with one another, however occasionally when atmospheric conditions are right (super refraction with a low lelve inversion being a good example) there has been documented cases of interference which occurs similar to your example. You mentioned that this was continuing to happen after the sunset spike which could suggest that the low level inversion after sunset was increasing the capability of ducting of the radar beam from GRB. Im not saying this was definitely causing the spike on the right but would be my first suspect.