When to visit
Of course, weekends will have biggest crowds. Specifically, Saturday afternoons are the busiest. Monday through Thursday before 1 pm is best for avoiding lots of people on the road and in the tasting rooms.
The month of June is actually a fairly quiet time.
|Highway 29 in southern Napa County|
Image from napavalleyregister.com
Where to visit
The south end of Napa Valley is closer to the SF Bay Area and is always busier than the north end. From the town of St. Helena south is where you'll find the traffic. Once you get north of St. Helena to Calistoga things magically clear out.
To the north there are a few large wineries that attract large crowds: Beringer, Sterling and Castello de Amorosa. But there are still many smaller wineries, from August Briggs to Zahtila, that won't be stuffed with other visitors.
|Calistoga. The quieter side of Napa Valley|
Image from menupix.com
Next door to Napa is Sonoma County. It can get busy at certain times also, but won't be as crowded as Napa. The general ideas here for Napa apply to Sonoma as well (fewer people on weekdays and to the north).
If this all still sounds too busy for you keep heading north to Anderson Valley in Mendocino County or over to El Dorado and Amador Counties in the Sierra Foothills east of Sacramento.
|Geyserville in Sonoma County. Even quieter.|
Image from 101things.com
With Napa and Sonoma Counties right next to each other you can visit both if your trip is more than a couple days duration. Pick lodging that is centrally located to both areas. Visit Napa on a weekday and Sonoma on the busier weekend.
|Image from vineyardandwinerysales.com|