The Weather and Climate in California's Wine Country

California's Northern Bay Area wine country—a larger region wine-making region that includes both Napa and Sonoma counties—is a year-round destination for both locals and visitors alike, in part because of a mild Mediterranean-like climate that makes it ideal for grape growing. Wine tasting is a popular area pastime from January through December, though winters can be relatively cold and wet and even, though rarely, produce a flurry or two. 

This guide to the area's local weather and climate will help you make the most of your visit, whether it's a harvest season celebration or a summer Sunday sipping chardonnay in Sonoma beside Balletto Winery's own baseball diamond. 

Fast Climate Facts:

• Hottest Month: August/September (84 degrees Fahrenheit)
• Coldest Month: January (55 degrees Fahrenheit)
• Wettest Month: January (4.37 inches) 
• Windiest Month: June/July (approximately 10 mph) 

Summer in Wine Country

In summer the throngs of travelers on holiday and those looking for a warm escape from San Francisco's endless fog make their way up to wine country, where temperatures are comfortable and rain is nowhere in sight. While it's a perfect time to take in the growing vines as they ready themselves for harvest, and the days are long and lazy, you'll also have to battle the crowds—which include an upsweep of out-of-town winery tours, ample farmers markets, and outdoor events like art and wine festivals, music in the vineyards, and Fourth of July celebrations. Heat waves can occur, but mornings and evenings are often cool, making them ideal times for enjoying a vineyard stroll or live tunes as the sun sets. 

What to Pack: Despite the warm days, any Bay Area resident worth their salt will advise you to bring layers, especially if you'll be returning to San Francisco later in the evening. Shorts, skirts, sandals, and tees are appropriate for the afternoon; carry a light jacket or long-sleeve shirt to throw on as the day progresses. A hat and sunscreen are also advisable, as well as a swimsuit and towel if you're considering a dip in Lake Berryessa or a visit to one of Calistoga's geothermal hot spring pools. 

Average Temperatures by Month: 

• June: 78 F (25 C) / 50 F (10 C)
• July: 78 F (25 C) / 53 F (12 C)
• August: 80 F (27 C) / 52 F (11 C)

Fall

For those interested in Wine Country's annual harvest season and the actual winemaking experience, fall is the ideal time to visit. The weather starts to cool a bit by October, though by then, the region's more than 800 wineries are already well into “crush season,” picking peak ripened grapes for sparkling and white wines, followed by reds, and getting them into the fermentation tanks to begin their transformation. Air is filled with the scent of freshly crushed berries, the leaves of the vines are turning brilliant shades of orange, red, and yellow, and most wineries are working at full capacity from early morning until late at night. It's an exciting time of celebration, with harvest balls and grape-stomping festivities, which means it can also be quite crowded. It's best to book any overnight stays early. Rain is a possibility, especially from October onward, and wildfires are an increasing occurrence, with the devastating Kincade fire taking place in 2019, and the Tubbs fire in 2017. 

What to Pack: Once again, layers are recommended—even more so in the fall when evening temps start to plummet earlier and earlier. Consider a light jacket, sweater or fleece, and a hat for cooler evening. Make sure to have an umbrella or rain jacket on hand for later in the season. 

Average Temperatures by Month:

• September: 80 F (27 C) / 49 F (9 C)
• October: 74 F (23 C) / 43 F (6 C)
• November: 64 F (18 C) / 39 F (4 C)

Winter

Things tend to be a bit slower in wine country during winter months, once the harvest season is over and the weather continues to cool. While temperatures don't typically fall below freezing, rains can be quite cold and heavy at times (February tends to be the area's wettest month), making indoor activities such as food-and-wine pairings a popular seasonal pastime. Crowds tend to dissipate during this season as well, meaning prices are more budget-friendly, and you can get more customized service, whether this means a one-on-one wine tasting or a private barrel room tour. There are also numerous winter activities, such as Calistoga's annual Winter in Wineries Passport, which gets you complimentary wine tasting flights at 16 wineries for $60 through the months of December and January; and the Napa Lighted Art Festival, a free nine-day celebration of light art and illumination that occurs each January. 

What to Pack: Dress warmly, including a rain jacket or warm coat and umbrella, plus a hat and gloves, which are musts during the winter season, when temperatures can get frigid. 

Average Temperatures by Month: 

• December: 56 F (13 C) / 36 F (2 C)
• January: 55 F (13 C) / 37 F (31 C)
• February: 60 F (15 C ) / 39 F (4 C)

Spring

If you're looking for relatively few crowds, inviting temperatures, and stunning natural scenery, spring just may be the perfect time to visit California's Napa and Sonoma counties. The weather is starting to warm, and the grape vines begin producing new shoots and tiny grape clusters. Rain starts to lessen, and the hillsides and vineyards become covered in mustard blooms in shades of orange, gold, and bright yellow, feeding the vines with substantial nutrients and providing a spectacular sight to see. Mild temperatures provide the perfect weather for picnicking, and many Sonoma wineries in particular are set up just for the occasion. 

What to Pack: Rain is still possible, so bring along an umbrella, and dress for the season: a light jacket, long pants or jeans, and a T-shirt, a long-sleeve shirt, or a light sweater depending on the day. Comfortable walking shoes are also a good idea, as you may want to take advantage of the agreeable temps with a stroll or hike. 

Average Temperatures by Month: 

• March: 64 F (18 C) / 40 F (4 C)
• April: 68 F (20 C) / 42 F (5 C)
• May: 73 F (23 C) / 46 F (8 C)

Average Monthly Temperature, Rainfall, and Daylight Hours
Month	Avg. Temp.	Rainfall	Daylight Hours
January	55 F	6.1 inches	10 hours
February	60 F	5.3 inches	11 hours
March	64 F	4.1 inches	12 hours
April	68 F	1.8 inches	13 hours
May	73 F	0.8 inches	14 hours
June	78 F	0.2 inches	15 hours
July	78 F	0.0 inches	15 hours
August	80 F	0.1 inches	14 hours
September	80 F	0.3 inches	12 hours
October	74 F	1.7 inches	11 hours
November	64 F	3.9 inches	10 hours
December	56 F	5.2 inches	10 hours