IN addition to the gross lack of emergency communications with the public that Yosemite National Park (and likely what most NPs have), there is a key, lesser-talked about hazard in Yosemite -- thick fog along roads -- especially in spring time.
As I was driving down at dusk from Glacier Point in Yosemite on April 24, 2012, several large and thick patches of fog drifted a long the narrow roadway.
I simply could not belive how I could only see about 5-10 feet in front of the car. Without barely being able to see the yellow line in the middle of the road and white line on roadside, I was completely blind.
When i t gets dark in mountaineous Yosemite, where there is little light poillution and when there is no moon, it is cave dartk, pitch black, and fog and compound the problem.
Luckily the 2 patches of fog only lasted about 45 seconds each and the roadway cleared, but if some areas of Yosemite are ever completely fogged in, good luck!
Snow is one thing, but fog can be worse.