David; a search came up this:

"Fruit cracking is more prevalent in the humid growing regions than in irrigated districts. Cracking occurs most frequently during periods of high humidity following rains. Absorption of rain water through the skin, coupled with the uptake of water from the roots, results in rapid enlargement of the fleshy cells. The internal pressure from the enlarged cells of the fruits creates a strain that cracks the skin. Differences in the thickness and composition of the cuticular layer of the fruits account for varietal differences in susceptibility to cracking. Russet is commonly associated with cracking in susceptible varieties."

The above info was found @: http://postharvest.tfrec.wsu.edu/market ... crack.html

The site describes specific varieties prone to "skin splitting," or "cracking," but I've had that problem from time-to-time with my Transparent Apples. In fact... they're dropping as I type; so I'm gonna have to look them over. Seems to me like an unusually wet Spring will bring this on; but humidity also looks to play a role. As much as I love Seattle... I think of it as even wetter than my Oregon home! But Summer's finally on