Though weather is generally mild all year, most visitors head for Napa in the cool of spring and fall. Summer can be somewhat hot during the day, but it commonly cools for great sleeping at night. In the winter, seasonal rains interspersed with bright sunshiny days turn the rolling hills emerald green, and the dormant vineyards come alive with brilliant color from wild mustard and other wild flowers, including purple lupine and crimson clover.

The best advice is to plan the timing of your trip to what your plans are. If you plan to hike or bike in the area – common activities in this natural and scenic area – plan your trip for fall or spring. If you don’t mind highs in the high 80s, then by all means head for Napa in the summer.  

Are you primarily planning to drive from winery to winery? Maybe add a day of shopping and spend some long hours eating? In that case, winter, or what the local's call "Cabernet Season," might suit you well. It's a time when the pace slows, the wines are aging in the cellars, and the local winemakers and grape growers have more time to revel in the natural beauty that surrounds them. Local chefs cook heartier foods that pair best with the region's famed Cabernet Sauvignon and other red wines, and the season's intermittent rains give reason to cozy up in front of a fireplace with someone special. Of course, dashing from car to winery door in the rain shouldn’t create too much havoc and might even add to the fun, and in between the rains you will be delighted with the clear, crisp sunny days that will invite you outside for a hike or bike ride, or a leisurely wander down a vineyard-lined country road. . 

Overall, temperatures are mild in Napa. January is the coldest month, with highs usually in the mid to high 50s. July is the hottest month. While highs can reach into the 100s, the average daily high in July sits around 85.