I have read through the posts in this string, and there are lots of good ideas here. I agree that Vancouver is an awesome city in an incredibly scenic setting, but keep in mind that the average number of rainy days in January is 20 for Vancouver and just 11 for SF. Not to mention the temperature difference... typical for SF in January is morning 10 to 15 C and afternoon 14 to 18 C.
If you are driving from San Francisco, Tahoe is certainly the closest - so then you just decide to stay at South or North Tahoe (once there, it's about an hour drive from one to the other with dry roads). The various resorts at North Tahoe are closer together than those 3 near South Tahoe, so it's a bit easier there to make choices according to the day's weather.
Then where to go? As some have stated, Northstar would be great for you as long as you avoid weekends (or at least Saturday - the crowds are much less Sunday). However, if you also want great views from the easy runs, and the weather is nice, Squaw is terrific since the easy stuff is on a high plateau-like area up high. Avoid Squaw on Saturday, and definitely avoid windy or cloudy days (Northstar is much much better in those conditions). I would guess that you will only have about half your stay at Tahoe, but even with 2 to 4 days you can check out more than one ski area or resort. If you have any flexibility about when you drive up to Tahoe, look for the best weather forecasts - opensnow.com is among the best resources. Have fun!