‘Atmospheric river’ threatens California wine harvest

Wineries in northern California are rushing to pick their white grapes ahead of anticipated heavy rainfall this week that could lead to disease.

Approaching rain is accelerating the pace of the harvest in California’s North Bay, with wineries frantically picking their white grapes to beat the storm that is forecast to arrive in the next few days.

Having already got off to a late start due to a cold, wet spring delaying the ripening of grapes by two to three weeks, the 2023 harvest is now likely to have an even bigger challenge to contend with.

An atmospheric river is expected to bring precipitation and high wind to the area, with winds of up to 30 miles per hour sweeping across the region. The bulk of the storm is expected to hit today and Tuesday.

For white grapes still on the vine, the rain increases the chances of botrytis, mildew and bunch rot taking hold.

Anderson Valley, home to some of the most sought-after vineyard land in northern California, is braced to receive almost an inch of rain in the coming days; troublesome news for major producers such as Duckhorn and Cakebread, which own vineyards there, due to the timing of the harvest.

Many winemakers in Napa and Sonoma have expanded their operations into California’s North Country in a search for affordable land with a climate more likely to survive climate change.

Total rainfall in northern California is expected to range from one to three inches in the lowlands when the atmospheric river hits, to as much as five inches in the coastal mountain ranges above 1,000 feet.

Hardier red grape varieties such as Merlot and Cabernet Sauvignon should be able to weather the storm, but producers are working through the night to bring in the more vulnerable Chardonnay and Sauvignon Blanc before the rain comes.

“The last thing you want is a heavy rain at the end of the harvest when we’re ready to pick,” Brooks Painter, winemaking director at V. Sattui Vineyards in St. Helena, told ABC News San Francisco.

The storm is also likely to affect vineyards in Oregon and Washington.

What exactly is an atmospheric river?

According to the American Meteorologist Society, an atmospheric river is a “long, narrow, and transient corridor of strong horizontal water vapour that is typically associated with a low-level jet stream ahead of the cold front of an extra-tropical cyclone.”

In other words, atmospheric rivers are ribbons of moisture that can carry large amounts of rain thousands of miles through the sky.