Hi newbee I had something similar happen just last week. I’m in BC and also a new beekeeper with a flow frame. I had a single brood hive and the FH super on top and it was bursting with bees so on advice of several people I added another brood box.
Then I got some bearding and after some reading and input from others on here I realized it was heat and humidity. As one fellow put it, they were just sitting out on the porch having a beer, keeping cool and cooling the hive.
Looking into the matter a little more I realized that I could help them by adding some ventilation at the top of the stack so I used an old bee box and put in some circular vents with screening. So I started with one brood and a super and ended up with two broods, a super and a ventilated attic 
I’m still getting bearding or clusters of bees around the entrance and some on the screened bottom board but not like before. All seems normal. We had several weeks of hot humid weather, thunderstorms and rain so I think you might have had a similar environment. Check out my other thread to see some pics and comments if you like.
http://forum.honeyflow.com/t/is-this-normal-behavior-after-adding-a-brood-box/7974