Right about now we are watching the latest in a wave of rain storms that have been crossing the state. We hope for rain, because 
the water supply needs it but also, and this might seem contrary because the Bees choose to take these rainy days off– it is benificial for the Bloom Set.
We measure the bloom based on strength and length. If Spring weather comes on too strong with a long string of sun filled days then the bloom period will shorten. Our pollinators won’t have opportunity to visit maturing flowers that can’t stick around.
So the occasional rain event is good as it helps to prolong the availability of the bloom. On the other hand, heavy rain or hail can destroy fragile newly formed buds and delicate flowers. A prolonged rain can cause mold or mildew; not helpful to harvest yield or for tree health.
A satisfactory Bloom Set is a predictor for the type of harvest to expect 6 months from now. We don’t always get perfect weather, or have ideal days, but we do have eternal optimism.
Is the strength of the bloom measured by density/coverage of flowers per tree?
Too my eye, visually abundant flowering with dense coverage would be satisfying. But, in reality a successful bloom is also measured by things like rate and longevity for the pollinator. Normally, 20% to 40% of the flowers set and grow into nuts that remain on the tree until harvest. The better the bloom the greater the [potential] yield.