So, a good trip to Napa generally has some planning involved if you want to coordinate your visits to the Wineries. Guaranteed the weather will hot. Not Humid hot; more like an electric hot blanket. There will be very little if any rain. In the months of May thru the beginning of August you will see the unripe grapes. In July the grapes change to their true colors. The harvest season begins in mid-August and spreads out into late October. This is the standard. All these times have something to offer on a trip to the valley.
Artesa – Napa – Cabernet Sauvignon, Chardonnay, Pinot Noir, Meritage, Albarino, Sauvignon Blanc
The most common way of getting around Napa Valley is by renting a car, grabbing a guide book, or some wine country brochures and getting on with it....and making it happen. It's a great road trip and it's an experience that's just great every time.
PS. If you are willing to make the effort and reserve and make appointments (I recommend you do a little of this)...There are places like Black Stallion, Buehler, Domain Chandon, Robert Craig, Inglenook and Robert Mondavi and Hess Collection all have excellent wine, tasting rooms, vistas for some unforgettable wine experiences.