Napa’s Valley’s famed wine region produced significantly fewer grapes in 2015, dragging with it the gross value of all grapes produced in the county by 24 percent to less than $550 million.

That compares to the previous year’s record value of $718.9 million on over 174,000 tons produced, also a record.

Average grape yields fell 30-32 percent compared to the previous year, with some growers reporting as much as a 50-percent decline in tonnage. Total tonnage of wine grapes harvested in Napa County fell 29 percent to just over 124,000 tons.

Steven Moulds, owner of Moulds Family Vineyard and president of the Napa Valley Grapegrowers, said his production was cut in half because of what growers call “shatter.”

That’s a condition in grapes where a significant weather event during bloom causes vines not to produce well. In this case an abnormally cool month of May led to “very poor” fruit set, including smaller clusters and fewer berries, according to Moulds.

“It varied from vineyard to vineyard,” said Moulds, who grows Cabernet Franc and Cabernet Sauvignon in the Oak Knoll District of Napa Valley.

Wine grape acreage in the county was down 1-2 percent on the year (whites more than the reds), according to the annual crop report produced by the Napa County Department of Agriculture.

Still, the value of wine grapes produced in the Napa Valley was never higher for many varieties. Cabernet Sauvignon grapes grossed the highest average of the reds at just under $6,300 per ton, very close to the price paid for Cabernet Franc grapes, at just under $6,100 per ton.

Cabernet Sauvignon acreage is the highest of the red varieties at just under 20,000 acres, a little under half the county’s total wine grape acreage of about 45,500.

Merlot, at over 4,700 acres, and Pinot Noir at over 2,700 acres, rounded out the top three most popular red varieties planted in Napa County in 2015.

Chardonnay grapes leads the white varieties planted in Napa at nearly 6,400 acres. Growers of the popular white variety grossed nearly $2,600 per ton in 2015, a 23 percent increase over what the wineries paid the previous year for the grapes.

Roussanne wine grapes, another white variety, grossed the highest price of all white varieties at just over $4,000 per ton. Fourteen acres of the variety are planted in Napa County, according to the annual crop report.

Sauvignon Blanc is the second-leading white variety planted in Napa County, accounting for over 2,800 acres. Growers of that variety were paid $2,012 per ton, a 5.3 percent bump from last year’s price.

Nearly 99 percent of Napa County’s gross agricultural value is tied up in its wine grapes. In 2015, Napa Agricultural Commissioner Greg Clark reported grape sales grossed $546.9 million on a total county agricultural value of $553.3 million.

The value of olive production, though minor in comparison to grapes, also took a big hit in 2015 as producers continued to battle the olive fruit fly, Clark said. Many minor producers chose to forgo harvest of their olive crop due to the reduced yields.

According to Clark, all of the county’s olive production goes to make olive oil.

Though acreage was down 52 percent to 140, average yields were up slightly as total tonnage more than doubled to 280 tons of olives on the year while gross receipts were cut in half to about $300,000.