I worked from home today, and am I ever glad that I did. Around 11am my biggest hive cast a swarm. They have filled five 8-frame mediums and the bees are working on the 6th. The queen was laying as high as the fourth box, with >4 frames of brood in all four bottom boxes. This particular queen is very prolific, and I knew it was going to be a struggle to keep up.
The swarm was approximately as big as a basketball. Thankfully they didn't go far, and I was able to shake them into a box. I added a frame of honey and a frame of mixed brood (some capped, some larva, some eggs) and gave them two mediums of drawn comb and one medium of foundation to draw out.
I'm not sure where the bees found all of the nectar already, but I have three (well now four) hives. Two have filled 5 boxes and are working on the 6th. The third has drawn out half of the fourth box and is filling it as fast as they draw it.
I'm sure the weather has a lot to do with it. Watch out, you could be honey-bound really early this year.