There is no bad time to visit Napa Valley. From late winter, when the vines are pruned and the tidy rows are ablaze with bright-yellow mustard seed, to the thrill of harvest, when wineries crush grapes and the air is filled with the sweet smell of fermentation, its charms evolve throughout the year. The peak tourist season is from August through October. Many wineries host harvest events, but during these months you will also pay the most for hotel rooms and spend the most time waiting in traffic or in lines in tasting rooms. If you picture yourself frolicking through the sun-drenched vineyard vistas that Napa is famous for, go anytime between May and October, when it rarely rains in this Mediterranean climate. But if you don’t mind a little fog and drizzly mornings, try winter, when wineries throw open their doors, reservations are readily available, and hotels are less expensive. Just keep in mind that many restaurants close in January and February.