Curious radar donuts

The radar antenna appears to be located in Nashville. Spreading centers like this are usually biological, such as a flock of birds. I have seen these on summer evenings when bats are departing a cave, but I think it's too cold for any bats to be flying. The radar specifically "sees" water, and is looking for incoherent (noisy) returns. A million bird wings would present a very incoherent return. The leaves on trees on a mountainside exposed to the radar beam will do likewise, especially if they are wet. The radar interrogator circuits work to eliminate presentation of coherent returns, such as billboards and semi trailers.

 

(https://)ground clutter
Mariners call it sea clutter.

Birds and insects being a part of "ground clutter" is one of the those inequities of being a lower order of herd critters.

Ashes are ashes...and dust is dust....but sometimes so-called 'wild fires' and aggressive plowing will add to the fun, because the volcanic stuff is mostly fairly dispersed.

The NWS used an S-band (2-4gig, IIRC) radar.
Fairly long for radar BUT it's about what you want for WX.

From the Wikis:
"A standard WSR-88D operates in the S band, at a frequency of around 2800 MHz, with a typical gain around 53 dB using a center-fed parabolic antenna. The pulse repetition frequency (PRF) varies from 318 to 1300 Hz with a maximum power output of 700 kW at Klystron output, although dependent on the volume coverage pattern (VCP) selected by the operator. All NEXRADs have a dish diameter of 9.1 m (30 ft) and an aperture diameter of 8.5 m (28 ft). Using the predetermined VCPs, NEXRADs have a traditional elevation minimum and maximum ranging from 0.1 to 19.5 degrees, although the non-operational minimum and maximum spans from −1 to +45 degrees. Unlike its predecessor, the WSR-74, the antenna can not be manually steered by the operator. WSR-88D Level I data is the recorded output of the digital receiver.[7] Spatial resolution varies with data type and scan angle – level III data has a resolution of 1 km x 1 degree in azimuth, while super-res level II, (implemented in 2008 nationwide), has a resolution of 250m by 0.5 degrees in azimuth below 2.4 degrees in elevation."

I was twisting STC knobs back in the day when dot.everybody went from analogue to digital radars.
The advantages are pretty clear in that digital receivers don't get droopy-eyed at 0300, and they don't have to take PCRs (to eliminate coffee.)
The DISADVANTAGES lie in the fact that there will always be edge cases where a sharp, trained, and motivated glass-eyed human operator, with knobs and buttons that are operated using the REAL digital method with real digits, and looking at the raw stuff will (can) out-perform SKYNET.....for now.....