It's hard to know where to start when trying to explain what went wrong during a beekeeping year, because the roots for a poor season start to develop during the previous year. The winter of 2011-2012 was harsh and cold, but bees can cope with the cold as long as they have enough food and their home protects them from the weather.
2012
The year started cold, then it warmed up quite quickly. The bees enjoyed this early hot spell and built up earlier than usual, so much so that some beekeepers were caught out and lost early swarms.
Then it rained, and rained, and rained.
In our part of the country it rained almost constantly from April through to December, this affected almost every possible aspect of beekeeping.