There's an old saying around Seattle that when Mt. Rainier wears a hat, you know it's going to rain soon.
I guess when it's wearing several hats, it's going to be quite a bit of rain?
The clouds, known as lenticular clouds, are formed when you have three ingredients: Warm, moist air that is just on the cusp of saturation, laminar flow (when you have winds constant with height -- as in little to no turbulence or shear) and something big to get in the way, like, say, the region's tallest mountain.
When the air flows over the mountain, it will create waves downstream where the air is now going up and down, and up, and down -- like ripples on a pond or waves on the ocean. When the air goes up, it cools a little bit and when conditions are on the cusp of saturation, that slight cooling is enough to create a cloud. When the air sinks back down again, an opposite drying effect occurs and the cloud disappears.
While to us it might look like the clouds are floating in place, in fact, the air is streaming through the cloud as it hovers there -- the cloud is just showcasing the right spot in the atmosphere where the air is undergoing its lift and sink. Sometimes this occurs right over the summit, giving the mountain a hat. Other times, it's just downstream.
To get the "stack of pancakes" look, you have this effect happening at multiple layers.
These conditions usually precede rainy weather around the Puget Sound region, and this time was no different. In fact, quite a bit of rain was expected along with strong winds Saturday.
Maybe the mountain knew it needed to dress in layers :)
For More Information:
What's that flying saucer cloud over Mt. Rainier?