Winter usually bring a lot of snow to these parks. As a result much of the area is deep in snow. The backcountry is not closed, it is just difficult to access and involves different challenges. The driving part of the parks is generally open, though the road to the Kings River portion of Kings Canyon closes. A recent change is the possible winter closure (from the first major snow, but possibly January 2 to April 1) of the Generals' Highway between Giant Forest and Grant Grove. With the lack of snow in 2012, the January 2 date was pushed back for weekends, but it was closed on weekdays until the first storm (mid-January). Since the potential closure, snow fall has been very low so closures haven't happened. My assumption is that this is part of a cost saving measure -- it is expensive to plow that road, and expensive to keep it clear of rocks through the winter and has always been lightly travelled in the winter. The closure makes it difficult to plan for a winter trip to both Sequoia and Yosemite very far in advance. Winter 2014-2015 was the driest (using April 1 snowpack) on record. This will make for a very dry summer for hiking and for the streams.
For planning trips, it is important to remember that winter conditions in California are controlled by the storms from the Pacific (or Gulf of Alaska). With no storm, it is clear and sunny, with a storm it can be heavy rain and/or snow. Plus, the type of precipitation depends mostly on elevation.
One big question is when does winter start and end? It varies, but you can expect snow on the roads and around the trees anytime from November to April (or even June). Cross-country skiing is usually available in the winter (some on roads, some on standard hiking trails).
Visiting in the winter can be trickier than Yosemite Valley in the winter because of the higher elevations. Chains may be required (CA has some specific rules on tire chains, generally if M+S rated tires are not sufficient, driving will not be easy anyway) and roads may be closed for periods of time. You are expected to have chains in your car whether you will be using them or not. This requirement is unclear with regard to cars where you sign the form that says the can cannot use tire chains. Weather conditions in Sequoia and Grant Grove can easily require chains (or even cause the roads to close completely for a time). Watch the weather and change plans if a storm is going to be there (or be prepared to drive and stay in the snow). Wusachi Lodge is far better for winter visits than the old cabins in Giant Forest. In Sequoia, only the lower elevation campground is open through the winter. In Kings Canyon, Grant Grove cabins (at least the Muir Lodge facility) and one campground is available all winter. The shuttles (in Giant Forest area and to/from Visalia) operate roughly from Memorial Day weekend through Labor Day.
|December, while cold, is early in the snow season so snow is not as deep as later in the winter.||By April, there is still snow, but depths vary.||Sometimes, June seems like winter.|