I had the same thing happen here! Freaked me out.
I live in the PNW though. Here we had a storm system roll in that caused extremely overcast days. Once the same came out the eggs picked right back again a couple of days later.
I know that's no help to you, but aside from the very dark overcast days there wasn't anything I could chalk it up to.
One big messy, noisy flock... Roughly 15 older members, 8 EE babies, 10 Cuckoo marans ( 10+ FBCM coming in April), 20 + Alohas. Yikes! Chicken math strikes again ;)
check out my eggzy stand! http://www.eggzy.net/egg-stands/349