It doesn't get much better than this!
The climate in the city of Napa, and Napa Valley as a whole, is delightful. There are no extremes as far as hot and cold weather, yet there are distinct seasons.
Summers rarely see more than a few consecutive days of weather over 90 degrees before the marine influence ushers in the lovely cooling fog, which rolls in quietly at night to blanket the valley and then "burns off" usually by mid-morning the next day. When the summer temperatures are in the 70's and 80's there is very little fog in the valley.
There is little to no rainfall from May through September. This is perfect grape-growing weather! The temperatures in the winter are quite moderate, with some nights falling below freezing but warming up nicely (50's & 60's) during the day. It's not unusual to have occasional days with 70 degree temperatures in the "dead of winter".
Most winters see no snowfall other than a light dusting of the white stuff perhaps once each winter, a novelty that everyone gets excited about. The surrounding hills get brown every summer and begin to turn green by mid- November. By February, most years, the hills become a gorgeous, "neon-green" color. Last year (06-07) was a near-drought year so we're hoping for more rainfall this winter. Normally, even during the heavier periods of rainfall there are only 2 - 4 consecutive days of precipitation. I don't have the figures for average rainfall here but there are LOTS of sunny days in the Napa Valley year-round.
Autumn is a favorite season in Napa Valley when many trees, as well as grape vines, display gorgeous fall colors in their foliage and the sky becomes a rich, vibrant shade of azure blue.