NAPA, Calif. (KGO) -- It may be Spring, but we're not through with winter quite yet. Some snow came down in the Sierra Wednesday and in Wine Country, there's concern about late frost ruining grapes.
"This one is probably the first stage of bud break, this one right here," said Juan Martinez, showing ABC7 News Cabernet Sauvignon grape buds in Napa, which like many varietals, broke early this year in February. "As soon as the bud breaks, you have to watch for frost protection."
RELATED: Frosty weather puts wine country grape growers on edge
Martinez has been working with wine grapes for more than 20 years. He currently works with Atlas Vineyard Management and says this time of year is tough since the weather sometimes gets cold enough to damage fruit and vines with frost.
"The buds can freeze and then after that all cells inside get frozen," he said. "You lose most of the harvest."
It is starting to cool down and has actually gotten cold enough this week that vineyards in Napa and Sonoma counties have had to turn their fans on.
RELATED: Napa residents, pets prepare for brutal, freezing weather
Thermometers on the vines send an alert to Martinez' phone when temperatures drop below 36 degrees, at which point he drives to the ranch to turn on the fans that circulate warmer air down to the vines.
Martinez has turned on the fans twice this year, both times in the past week.
Wine country is at risk of frost until June.
Click here for more stories, photos, and video on wine and wine country.
North Bay wine growers concerned about late frost for grapes