Finger Lakes sybarites love to romance their regional vintages, but the reality is that grape growing is crop farming, and crop farming is largely weather dependent. With a mild central New York winter suddenly returning to normal or below-normal temperatures, area grape growers have reason to be worried for their crops.

Because of water retention at warmer temperatures followed by a sudden freeze, this year's harvests, from Chardonnays to Concords, are threatened by damage to buds that will produce this summer's grapes, say experts at Cornell's New York State Agricultural Experiment Station in Geneva, who are keeping a close watch on their vineyards.

"The main concern is with buds freezing," said Tim Martinson, senior extension associate at Geneva. Mild weather has caused grapevines to retain water and buds are more vulnerable to freeze-kill at 4 degrees higher than is typical. "The plants need to gradually lose water and acclimate. And with warm, moist conditions followed by unseasonably cold temperatures, that doesn't happen."

A sudden deep freeze could cause cells to burst in the vines' trunks and buds. In 2004-05, for example, temperatures suddenly plummeting to minus 10 degrees Fahrenheit destroyed 75 percent of such cold-sensitive grape crops as Riesling, Chardonnay and Pinot Noir, as well as many stone fruits.

A sudden cold front this week is sending overnight temperatures down into single digits at least once, with daily temperatures in the 30s and lows averaging about 14 degrees, said Mark Wysocki, state climatologist with Cornell's Department of Earth and Atmospheric Sciences. There will be a warming trend Wednesday and then unseasonably to seasonably cold temperatures Friday, Saturday and Sunday, he said.

"We're in for a bumpy ride for at least the next week or longer," Wysocki said.

That's not welcome news for area grape growers.

While all varieties can be damaged by sudden freezing, such varieties as Merlot, Pinot Gris, Cabernet Sauvignon, Pinot Noir and Gewürztraminer are particularly susceptible, said Martin Goffinet (GOF-fin-nay), senior research associate at the Geneva station. The vinifera varieties (those that originated in Europe) and many hybrid varieties (many developed at Cornell) also are particularly vulnerable to winter cold snaps because they tend to acclimatize slowly, he said.

Bud growth actually begins the year before the grape emerges, Goffinet explained, so the following summer's embryonic buds are already growing while the vine producing the current season's harvest is in bloom. Under normal conditions, buds acclimatize to gradually cooling temperatures throughout a seasonable winter. American varieties, including Concord, Delaware and Catawba, acclimatize quickly but are vulnerable to spring frosts because they come out of winter dormancy earlier.

"Typically the first week of February is the coldest week with temperatures dipping down to zero or minus 5 Fahrenheit," Goffinet said. "In a typical year, vines seem to do okay; they've had lots of prep, and the buds are dry. We are concerned right now but we haven't yet had temperatures that can kill the vine. But if the trunks fill up with water, and there's a sudden hard freeze, they can actually split."

The most susceptible grape varieties, he said, will need about one to two weeks of cold (but not bud-killing cold) temperatures to regain the winter hardiness they would typically have at this time of year. Goffinet also said stone fruits -- apricot, peaches and sweet cherries in particular -- are also susceptible to warmer temperatures, and any precipitous drops in temperature "are going to be problematic for next season's crop."

"Between the poor fall ripening and warm winter temperatures, we're hoping we don't see any below-zero conditions any time soon," added Geneva researcher Steve Luce, who conducted freezing experiments on buds Jan. 3. "Sometimes all it takes is a one deep freezing event to cause damage."