I hate to make an opinion from miles away without my own inspection, but
surely there are two possible causes, and maybe three.
My first choice guess would be Tracheal mite.  Your description and time of
death is very typical.  Was the colony treated with menthol in late August, or
had grease patties in the brood chamber for the past 6-12 months?
My second choice would be a dead queen.  A queen can die in any of the 12
months of the year.  If she was  new queen after June, she probably was poorly
raised as a supercedure result and maybe poorly bred.
Your description of the mold, implies these bees died some time ago, maybe in
December.
My third choice is:  How strong were these bees in October?  A colony weak in
bee population in October and November does not have good chance of getting
through the winter.
Lastly:  It is preferable to face a colony southeast, not north.  Southeast is
the warmest part of a hive (that is where the cluster of dead bees was), while
facing north gets the northwest winds, rain, and snow blowing in.
I hope this helps.  See your bee inspector, and READ, READ, READ, and attend
bee meetings to LEARN.   In 1998, no longer can bees be kept like your Daddy
did for a lot of reasons with the Tracheal mite and the Varroa mite being the
#1 reason.
George Imirie in Maryland - 65 years with bees