If the conventional wisdom about chill hours is correct, this year will be bad for stone fruit in the Central Valley, but not as bad as last. Peach, plum and nectarine trees need 900 to 1,200 hours of temperature below 45 degrees over the winter to produce an abundant summer crop, according to long-standing orthodoxy. Last year, the Central Valley got no more than 600 chill hours, and this year eked out 800.

As it turns out, the conventional wisdom about chill hours suffered far more damage than the fruit trees in last year's warm winter. The Central Valley packed out an all-time record crop of peaches and nectarines in 1996 - a whopping half a billion pounds of each. "A lot of us are still scratching our heads as to how that happened," said David Parker, director of marketing for the California Tree Fruit Agreement, the marketing association for peach, plum and nectarine growers.

Plant scientists have a couple of possible explanations, both of which boil down to the fact that the University of California may have been counting chill hours the wrong way. It seems that Cornell University has a method of counting that ignores spikes in temperature during the day. By Cornell's reckoning, the number of chill hours in the Central Valley last year was about right.

The University of Utah has yet another method, which puts a premium on the number of chill hours in the early part of the winter through the first week of January, largely ignoring deficits or surpluses for the rest of the winter.

However you count them, the Central Valley this year once again seems to have gotten enough chill hours for a good crop of stone fruit. The trees were blooming and setting fruit at a healthy rate in February into March, said Parker. Some of the early varieties were struggling, and their crops might be erratic. But the mid-season varieties were looking good, he said.

The new thinking about chill hours is good news not only for consumers looking forward to abundant summer stone fruit after winters that seem to be getting warmer. It also could give California farmers new crops to consider -- or reconsider.

"We may have to rethink a lot of decisions we made about what we can't grow," said Ben Faber, a fruit expert with the cooperative extension service in Ventura County. Agronomists may also now be able to explain some heretofore unexplainable phenomena. Take, for instance, the amazing performance of Fuji apples -- believed to need a minimum of 800 chill hours each winter -- in an orchard near the Ventura County town of Somis. They color up nice and red much earlier than Fujis in prime apple country further north, even though the winters in Somis are supposedly not nearly chilly enough, Faber said.