The 101 is a major highway and most, if not all, is divided and much is limited access "freeway." It's unlikely to have serious weather related problems. Any of the other "mountain" roads could have more serious weather impacts. The coastal side snow is unlikely and almost never a problem. The Sierra/Cascade side would have similar issues to Reno, temporary storm closures although 44 and 299 are at their highest points lower than I80 over Donner and won't get that kind of snowfall nor traffic.
Generally the storm patterns are predictable so unlikely to be surprises. Given the large numbers of fires, heavy rains can result in local flooding and mudslides in fire areas and downstream. Aside from Big Basin, south of San Francisco, haven't heard of fires impacting the redwoods parks. That just means they haven't made the news so smaller fires may have caused damage. One advantage, aside from being in the rain when it's raining, is the rain wets down and cleans the foliage and trees, deepens the colors and gets rid of the dust and dirt that built up over the hot dry weather.
The 1, although along the coast, is kind of a mountain road and while almost never gets snow, can get serious damage from rains, flooding and mudslides. It's a beautiful but slowish drive. Also, if you consider the the northern portion of the redwoods country up around Eureka, it's redwoods and logging history dominated. Towards the southern end, you get into the wine country. It would be well after harvest and fall colors but has some added options for visiting wineries, tastings, restaurants, etc.
Right now, that area is impacted by fires and Covid restrictions and not sure how that will change by December. Hopefully indoor dining, beverage service, tours, etc., will be back on.