part of a wave

We've been awash with American Painted Lady butterflies floating around town. I just figured they were always here, but having been hunkered down in the rain for so long were all coming out at the same time. But in today's paper I read that a Denver weather radar picked up a wave of them that was 70 miles wide! Apparently they are migrating to the south western US and northwestern Mexico. It's a treat to see so many.
Here is one with its wings closed so you can see the underside, instead of the Monarch mimicking orange and black topside.