I love the Napa Valleythe last time I was there it was summer, and the weather was great. The only problem-too damn crowded. I would like to know if the climate is OK in late fall-the rates are lower, and the crowds much less. Is late fall a good time to go to Napa?
NoCal is generally pretty nice, but it’s hit or miss. There will be a mix of nice spring like weather and shitty rainy days, with the percentages lying on nice. Here in SoCal, it’s a beautiful 75°, and I think the weather is probably similar (weather underground says the high in Napa Valley is 76° today) I’d go ahead and just do it, because you can still go wine tasting if it’s raining. It’s also quite spectacular just after a rain.
Usually, it’s wet and rainy or cool (50s/low 60s) and dry. It won’t snow, but it can get very cold (down into the 40s, with wind and rain). It can also be unseasonably warm. If you want warm weather AND fewer crowds, I would recommend going in the early fall, like mid September-early October, which is actually the warmest time of the year in Northern California.
FTR, I grew up in Sonoma County, which neighbors Napa County to the west.
A definition of “very cold” that amuses us Minnesotans (and probably most Canadians). 
Our version would be 40…below. About 80 degrees difference.
Oh, I LOVE one-upping over weather. A conversation that never grows old, truly! So glad to amuse you. I live in Michigan, by the way, a place famous for its mild winter weather.
Seriously, I’m talking about going on vacation. Do *you *want to go on vacation somewhere chilly and damp? I dunno, maybe you’re into that kind of thing.
We didn’t make it over into Napa, but we spent a few days in Sonoma this May, and it was perfect. Weather was in the 70’s and low 80’s, sunny, clear, utterly gorgeous. And there were no crowds to speak of at all. I understand it gets pretty crazy between Memorial Day and the end of the harvest season, both there and in Napa.
Every time I’ve been to Napa, it’s been in the winter. It’s usually nice enough. It can be rainy and chilly, but just as often, I’ve had sunny weather. I do this primarily to avoid the crowds, and I’ve always had a good time. There are usually some people, but not a lot (especially during weekdays), which I like because the vineyard folks have time to talk to you.
So yes, some of us do deliberately take vacations somewhere that can be 40 degrees and rainy, and for good reason.
The above posts describe the climate pretty well.
I’ll also mention that the vineyards themselves are very pretty at that time of year. The vines are all dormant but the natural, fertilizing foliage that they plant between the vines are in full bloom. This is usually mustard which blooms with yellow flowers so you have these big fields full of yellow with dark stripes running through them.
Even in the off-season Napa is very picturesque.
Try searching on ‘napa winter’ on images.google.com and you’ll see what i mean.