At least 11 people are reported to have been killed as a result of the wildfires, with hundreds of homes, businesses and vineyards destroyed.
A number of large wildfires broke out over the weekend and this week, fanned by high temperatures and dry conditions, spreading over more than 115,000 acres.
The extent of damage to vineyards is not yet clear, but the fires are expected to have a serious impact on the industry.
California is by far the largest grape and wine-producing area in the US, accounting for around 85% of the country’s total output. It has 4,581 wine producers and 560,000 acres of vineyards, generating close to $71.2bn in total economic activity each year.
Wine tourism is also a significant part of the industry’s impact: the ‘wine country’ regions generate 23.6 million tourist visits and $9.7bn in annual tourism expenditures.
The fires coincide with harvest season, with grapes typically picked from August to early November. However, Wine Institute - the body which represents the California wine industry - says that fortunately the majority of grapes have already been harvested.
As well as destroying vineyards, smoke can damage unharvested grapes, leading to unpalatable wine.
The Wine Institute says that it will not be possible to assess damage until fires are contained.
"Our thoughts and prayers go out to all of those who are impacted by the fires, and we are very grateful for the firefighters and first responders who are working tirelessly.
"We have been in touch with the winery organizations in Napa, Sonoma, Mendocino and Lake Counties to offer assistance. Right now, they are focused on ensuring the safety of their communities, offering assistance and gathering information.
"Accurate assessments of vineyard and winery damage cannot be made until the fires are contained. It is too early to know what effect the fires may have on the 2017 harvest or wines from the vintage of these regions. Fortunately, the majority of grapes were harvested earlier in the season."
The Napa Valley Vintners reported Tuesday that preliminary reports show at least four physical wineries belonging to its members have suffered total or very significant losses. At least nine other members so far have reported damage to their operations.
"We have yet to hear from some members in the most vulnerable areas of the valley, including along the Silverado Trail, in Calistoga and in the Mt Veeder/Partrick Road/Henry Road areas."
There are also other wineries that have not yet been able to access their properties.
Other significant impacts include power outages and communication challenges.
"Complicating matters is the fact that it is harvest season in Napa Valley," continued the NVV. "However, we estimate that 90% of the grapes were picked before the fires started on Sunday night. Wineries able to assemble crews and safely get to their vineyards are continuing to harvest grapes.
"Power outages and the inability of employees to report to work also have also created challenges for wineries, especially for tasting rooms. However, most wineries have emergency generators, which has helped maintain production capabilities.
"It is too soon to tell how the fires and related challenges will impact this year’s vintage overall. What we do know is that of the grapes remaining on the vine, it is almost all Cabernet Sauvignon. Our winemakers report that this thick-skinned variety, fully-developed and ready to be picked for the 2017 harvest, is not expected to be impacted by the smoke from the fires.
"No matter the circumstances, our winemakers remain committed to upholding Napa Valley’s reputation for making some of the world’s finest wines and they will do everything possible to ensure the highest quality wine-making for the rest of the 2017 vintage."
State of Emergency
On Monday (October 9) Governor Brown declared a State of Emergency in Napa, Sonoma and Yuba Counties – all well-known wine producing regions.
A statement issued by CAL Fire, California’s fire and emergency response department, reported that an estimated 1,500 homes and commercial structures have been burned as the wildfires spread across more than 115,000 acres.
“Firefighters have been challenged with winds gusting in excess of 50mph causing extreme rates of spread and volatile burning conditions,” said a report, referring to conditions over the weekend and on Monday.
The winds have since decreased but local winds and dry conditions continue to pose a challenge to firefighters.
Red Flag Warnings in southern California due to gusty winds and high fire risk remained in place yesterday morning, but were due to end later on in the day. (Red Flag Warnings are the highest alerts).
Historically, October is when California experiences its largest and most damaging wildfires, and the department urges residents to remain prepared for wildfires.
Cal Fire posts updates on wildfires, evacuations and road closures here. It has also published a statewide fire map, as below.