Same thing happened to my bees. Today was slightly warmer (50 degrees), low winds and they were out in force for a couple of hours.
As soon as the temps dropped a bit they were back to staying in the hive.
We have been having highs in the low fifties and lows in the upper thirties and low forties with fairly strong winds.
Is it true that bees will stay in the hive when the temps are below fifty?
It seems like that is the magic number for my bees. Seems true on windy days too.