Well, I haven't found more info (so far), just more listings of essentially the same article. But one of these relistings had information about some other interesting sky phenomena, popcorn clouds (called Mammatus clouds), that've been happening lately, and here's more info about it.
Here's a photo from near sunset on the 21st of June taken from my window. Not quite popcorn clouds, but similar.
And here are some really neat, unusual clouds, taken in the last two weeks of June.
This explains why I've been seeing such amazing sunsets for the last couple of weeks. We've been having days that are quite warm, consistent with Summer weather, and that usually inspires thunderstorms with their spectacular cloud formations around sunset, and I thought that's what was causing it. But it might not be the only cause. Here's one of the recent sunsets, from the 23rd of June.