Reasons for cherry crop failure in addition to low chill

At a family member’s house in the Bay Area, they had a poor cherry crop this year after a phenomenal crop last year. I had a better crop in San Diego (though different cultivars). What is the best explanation?

It does not seem to be chill. It was cold this winter, and the UC chill hours models were roughly the same (slightly worse, but well above threshold needs).

Interestingly, the lowest chill cultivars fared worst (Cristobalina, Minnie Royal, Royal Lee, etc). The highest chill cultivars look to be slightly better, and may do better still (will know in a couple weeks).

Furthermore the high chill Baby Crawford peach has a reasonably balanced crop on a young tree. So it doesn’t seem like chill was the problem?

What other things cause cherry crop failure in a marginal chill area? It has been very dry the past 6 months. And they had the same funny weather where it got colder in February instead of warmer. The bees seem a little less active too. Not alternate bearing after a massive crop last year? Curious if others, especially in Northern California, have insights.

Not from your region, but annual production is partially based on levels of stored energy and requires a certain amount of new wood every season- a heavy crop can upset the energy balance and if there is a dearth of new vegetative wood it indicates that. Leaf to fruit ratio cannot be slanted too far to the right if a tree is to have the energy required for fruit bud creation that flowers the following year. Did the trees have normal bloom this spring?

You say weather was dry, but even drizzle when cherries are in bloom can cause blossom rot.

In the east coast, annual production, especially of apple trees, seems to be affected even by cool cloudy weather in the spring. If a tree is investing in a heavy crop under such conditions, even adequate thinning and fairly vigorous growth will not assure a crop the next season according to my own observation (not science, just a strong hunch based on a certain level of knowledge of fruit tree biology and anecdote). However, the main cause of crop loss in our region, outside of bird and squirrel predation is wet conditions while trees are in bloom- I would guess warm and wet is the worst. Sites with near dawn sun and good air circulation most reliably produce crop.