For a really good fruiting year you need a whole set of circumstances. The first is that the previous autumn is warm and long, so that the fruiting wood has plenty of time to grow.
Then you need the previous winter to have been properly cold. A lot of fruit trees are programmed to only produce fruit after a truly cold winter. With the trend for warmer winters, this spark to fruit production has been lacking.
The cold also kills off huge numbers of the pests and parasites that can destroy the flower buds and the nascent fruit. It cleans the environment into which the new blossom will emerge.
A late spring is also good. Then everything is synchronised – the bees and other pollinating insects and the flowers – all emerge together in one great whoosh. What you don’t want for a bumper harvest is a stop-start spring – warm and bright, then winter again.
Each time that happens, it destroys some of the already pollinated flowers (and so the fruit), and gradually depletes the harvest. Nor do you want any harsh storms or frosts that can destroy the blossom and give you no fruit at all.