We are in the process of signing our vacation list at work. I thought that this year I would like to do a California trip up in the bay area, including a sidetrip or sidetrips to Lake Tahoe, Yosemite, Monterey or the wine country. I will take a week and a half to two weeks for this trip and do not prefer to travel during the summer (We don't have kids and prefer to travel at a less popular time). I have vacation scheduled in late April/early May, mid-September, early November and at Christmas time. Which would be the best time to visit in this area? Any suggestions on what to include in a week and a half vacation compared to a two week vacation?

My vote would be mid-September...after kids return to school.
Weather is great, tourism tails off.

BTW, I think the Bay Area and environs (much of which you mentioned) offers the richest set of travel opportunities of any single destination in the USA. The variety is so wide. There's so much to see that's unique and memorable.
If foreigners can only visit one area of the US in their lifetimes, I think northern CA is the place to go, provided they have at least 10 days.

I'm a warm weather person, so on that basis alone, the mid-September option is the only one I'd consider, especially for Tahoe and Yosemite.
Kay's points are all excellent.
Are you driving? Flying and renting a car? If flying, don't miss the opportunity to fly into one city and out another, usually within California at no additional charge, or possibly SF/Reno in and out. Although car rental drop off fees picking up or dropping off in Reno might be a killer. Sacramento might be another option for flying into or out of, starting or ending with Tahoe and Yosemite.

Just another Californian checking in to say, "September!"

Lynette

...and another Californian votes for September. Second choice would be your April-May time frame.

Welcome to CA!

Another Californian voting for September

Another Californian voting for September. Secifically, after Labor Day weekend.

As someone fortunaate enough to live Northern California I will add my vote for September. Great time to visit our area.

The spring vacation sounds the best to me. It offers very pleasant weather (mild or warm temps, breezy, some showers - maybe), lush green landscapes with blooming trees and wildflowers, vibrant waterfalls in Yosemite, and fewer tourists than in Sept/Oct.
I've lived here for decades, and Spring is my favorite season - late Feb/Mar/early Apr being optimum, IMO. If you like warmer (probably hot) temps with less chance of rain (or weather of any kind), a dried-up brown landscapes and mtns with no snowcaps, then go for Sept. As far as time scheduling, it only makes sense that if you want to go to all those places, (SF, Tahoe, Yosemite, wine country, Monterey), which is perfectly fine, then you need to allow 2 days for each place for a 10-day trip.

I also live in Northern California and would say to go in mid-September. The previous poster's reasons to go in Spring are valid, but it's still kinda risky. You might get cold weather and rain. May would probably be better, still risking some rain, but you'll get some nice sunny days.

Based on some of Celine's previous less than pleasant statements on other threads, I would take her opinion with a grain of salt. Mid-Sept. tends to be hot. Early May would be my choice.

Although September, as are many months, is a very fine choice of month to travel here I would agree with the poster directly above in suggesting April or May.

I say this because CA's rainy season is in winter. Although San Francisco is gorgeous year-round, the side trips you take as well as the scenery in general is much greener and fuller in Spring. By September much of the natural sagebrush, chapparal, and natural grasses die off and turn brown. Then again, as I type this I remember a late summer drive I took from the Sierras to my home here in Los Angeles, and the rolling brown grasses in Sonoma were spectacular. Nevertheless, I'd avoid the mid-summer (June-August) and stick with Spring or Fall.

I just returned from a New Year's holiday in San Francisco and the city is as enthralling as ever! Stayed at the Westin St Francis right on Union Square and got a room for $98 per night! Admittedly, it is an old hotel and the room was cramped to say the least, but the furnishings were very nice and the location perfect for exploring SF... cable car ride away from Fishermans' Wharf, a healthy walk to the restaurants in the direct vicinity and to the financial district. Absloutely loved it! Happy travels and welcome to CA!!

I agree that fall would be a better time to visit San Francisco, as it is usually a bit warmer, but either spring or fall would probably be fine. Though I think spring would be a much better time to visit Tahoe or Yosemite.

San Francisco is great year round, in my opinion. But if you are doing Tahoe and Yosemite, my vote would be for spring. Sure, it will be cooler than, but if you are expecting that, you plan for it and move on. September outside of SF or the mountains is not only hot but humid. Besides, by September, the waterfalls at Yosemite will be practically non-existant. The best time to view them is in spring.

Whichever you choose, have fun and enjoy!

Steve,
After 40+ years of living in the Bay Area, I'd consider any of your chosen times to be good for different reasons.

April/May has green hills, wildflowers and mild spring weather going for it. I love the back roads of Napa and Sonoma at this time of year - there are fields of wild iris and poppies in bloom.

Mid-September, as previous posters have pointed out, is our warmest and driest time of year. If you are planning a long drive on the coast, you probably won't be dealing with fog.

November and Christmastime have their advantages, too. You won't be competing with many other tourists, B&B prices are way down, and if you are from a severe snowy climate, you'll find our comparatively mild winter a relief.

If I absolutely HAD to choose, I'd probably say the first week of May.