2/25/23 KTWX Unknown Anomaly

Around 16:45z today on KTWX, an interesting signature was found converging onto a lake near Jeffery Energy Center near the Emmett Township in Kansas. Around 22:40z, a large number of signatures was found dispersing from the area once converged on.

This sparked some discussion on Twitter, as the irregular signatures did not match the orthodox measurements of birds (more dependency in the azimuth for ZDR), and moisture plumes from the plant, as mentioned by @jmkurdzo

I attached a couple of links to some of the tweets that Kurdzo made, notably with the ZDR/PhiDP signature and ZDR distribution. It would be great to see what others on this page can come up with to fit the anomalies seen on KTWX today.

Here are some PPIs/pseudo-RHIs from the Level 2 data:

Beginning of the higher reflectivity signature


Peak reflectivity scans

2258 UTC


2315 UTC


I think putting together a blog post on this would be pretty neat…

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The discussion on another Twitter thread primarily focused on why ZDR was so noisy. There were values ranging the entire current viewable range on RadarScope (-7.9 to +7.9 dB) as well as some values that were touching the -13 dB and +20 dB edges in the raw Level-II files in Build 21 of the ORPG (hence the histogram I plotted above). This was really perplexing to me because I would think the (obvious) target of birds would not have (a) such extremely low ZDRs, and (b) such a high spatial standard deviation of ZDRs.

What convinced me that these were, in fact, birds, was @swnesbitt mentioning the scattering regime. Some local folks in KS had mentioned snow geese, and Steve said that if the targets were that big, they’d be well into the Mie and even optical regimes. This would very easily corrupt ZDR in terms of how we typically use it for analysis. If you keep this in mind as part of the puzzle, the rest of the data match up with large migratory birds in my opinion.