Nice comments from everyone.
I did definitely see the shadow bands appearing against an off white plastic tent.
Took a photo that shows nothing. These are mysterious and poorly explained and nearly impossible to capture in a photo.
BTW, I counted on the NAM cloud cover maps at instantweathermaps.com. For all the NAM hatred, these maps did quite well for me.
During the excitement, I mis-programmed my Nikon for ISO 3200 at 1/4000 second. Modern cameras are amazing, it still captured an image.
Diamond Ring for y'all.