Trying To Make Sense Out Of The Sky

Frank sent this from his flight yesterday from Seattle to Sacramento. I replied:

That’s really cool. It looks like some kind of coil. Is that central part a plume of some sort, some kind of terrain barrier, or just cloud?

He responded:

It's interesting that the photo does look like a corkscrew, although I don't remember it looking at all like that when I saw it. Rather, what I thought I saw was a blanket of solid clouds with a series of regular humps, like speed bumps, along the blanket (convection cells?). For a moment, I thought I might get a photo of that, but it was just a little too far behind the plane by the time I realized what I was seeing.

It was solid overcast leaving Seattle around 5 pm, but as we got toward Sacramento, from around 6:30 PM or so, there was a spectacular cloud show with multiple layers of cumulus, stratus, and all manner of shapes, a few with anvil tops. We were flying in and around those for maybe 15 minutes. The blanket (above) ended quite abruptly with a patch of clear sky around Sacto.