The average temperature in Napa in August is 72 with a high of 90 and a low of 55.
August is high season in The Napa Valley. It's a beautiful time of year. Hotels will book early and full.
Some wineries and tasting rooms do not allow anyone under 21. And some require appointments. Please call ahead.
The Pacific Ocean is 1-1.5 hours from Napa. The coast is majestic and worth seeing if you have time.