You could just wait and see.
Hello and welcome to the RTA forums !
It's impossible to predict what the weather might be doing right at the time you travel but you are right in thinking the weather might be a problem at higher elevations, but not necessarily. Travelling at this time of year does have it's advantages, the main one being the crowds have disappeared and lodging is more readily available, giving you the opportunity to research all your options, but leave them open to change rather than having a set itinerary. Yosemite and Sequoia can be wonderful in November and during the early part of the month especially, you could see some reasonable conditions. With 3 weeks you have all sorts of possibilities, including heading North of SF to the Redwoods State and National parks. So if you would feel comfortable doing so, why not just wait and see what the weather is like once there.