In my experience, anything that reduces the leaves, and particularly the spur leaves, access to photosynthesis can lead to a crop reduction or failure. I've discussed this with a commercial grower and he believes a cool wet spring even following flowering reduces fruit set for this reason.

I believe energy stored towards the end and produced at the start of the season may have most affect on fruit set.

We had a late summer monsoon here season before last and apple set was somewhat light although leaves did not defoliate on fruit trees. More surprising was that for the first time in memory the oaks had very few oak nuts (I refuse to call them acorns) for two consecutive seasons.

It's making the wildlife absolutely frenzied for food this year to the point where they are shaking bait out of bait stations (never happened before).

Normally oak nut harvest is reliably bienniel.

"Normally oak nut harvest is reliably bienniel."

That's interesting. Here oaks produce annually. The only exception is sometimes if the weather is extremely dry, the oaks will drop their nuts.

More evidence that bienniel bearing is strongly influenced by the length of the growing season.

I'm curious, why the aversion to calling oak nuts acorns?

What I should have said is normally a poor crop is followed by a heavy crop. Here late frosts do occassionaly wipe out the crop which sets up a bienniel pattern that can continue for years. Frosts were probably not the issue this time for either short crop, however.