Update Tuesday November 23rd.--The weather changed significantly cold and snow over the last weekend and cold subfreezing weather is prevalent throughout the Puget Sound and expected to last through Wednesday before warming Thanksgiving Day and into the weekend. But the cold and snow will continue at Mt. Rainier where snow is almost everywhere in the NP, with over a foot at Longmire and over 4 feet at Paradise.
This means while the NPS will make every effort to clear the road from Longmire to Paradise and the parking lot, it may well be later in the morning early in the week and providing no new snow by Thanksgiving, near normal Thanksgiving Day and into the weekend. You can still enjoy the snow and place, just be ready for really cold (subfreezing) weather and snow.
Original post.--So, you live in the Puget Sound area or are travelling here for the holidays, and you have the time or want to take the time to visit Mt. Rainier NP. The first and obvious question is, how do I get there? Locals already know and visitors guide or information service at hotels can provide the information. You can also get the latest information on everything Cascade or Olympic Mountains for the USFS lands and NPS national parks at the USFS-NPS ORIC.
This is important because once winter settles in, which it has already with an early snow in late October that didn't melt and more snow this week (Nov. 18-21) leaving 3-4 feet of snow above the 5,000 feet elevation and less down to about a foot at 3,000 feet elevation. In short, expect snow and enjoy it. With only one entrance open to inside the NP (Nisqually entrance to Longmire and Paradise), you're very limited to that road and activities along it.
There are two other entrances, the Mowich Lake and Carbon River entrances in the northwest quadrant. Both of these entrances are closed at the NP boundary and entrance, respectively. The Mowich Lake road from the boundary to the lake and campground have snow and the Carbon River doesn't but expect to encounter snow quickly once off the valley trail to Ipsut Creek campground.
That said, you can get an overview of the area to and around Mt. Rainier NP as well as a description of the roads, access, conditions and activities, for which the latest is also available via a map. The road to the Nisqually entrance has quite a few lodges and motels from Elbe to the entrance and mostly near Ashford.
So, you've decided and you're on the road, what's next? Well, expect a wait and maybe a cancellation of access to Paradise. The former is normal during winter and the latter is rare on weekends and holidays as the NPS tries to clear the road to Paradise. You can get more extensive information on winter in the NP with a map of the general information.
The road between Longmire and Paradise is controlled at a gate just east of Longmire. It opens to uphill traffic after the snow is cleared from the parking lot at Paradise and the road down to the gate and Longmire. This usually happens about 10 am. The gate closes to uphill traffic at 4-5 pm during the winter. In addition all people without an overnight winter camping permit at Paradise (specific parking area) are required to leave nightly.
So, you're there, or at least waiting in line with the other going to Paradise (always loved those words, "road to Paradise"), what's there to do? Well, easy, winter. Ok, more please. The only facilities are the visitors center which is open 10 am to 5 pm (all four days of this holiday. The snowplay area does not open until there is at least 5 feet of snow at Paradise (not usually during Thanksgiving Day holiday). Otherwise, there is just the beauty of the mountain and NP.
In the end, it's a great road trip if you want snow and Mt. Rainier. Well worth the experience and memory if you don't get there or to snow very often. I can only add to drive carefully, especially if you don't have much experience driving in snow, and go prepared for the trip, the wait at the gate and the trip up to and down from Paradise.
Have a good and safe trip and enjoy the mountain and NP.