one tip: you need to be careful to not blow out the white snow, like in the first image. This is even more difficult when you have dark trees in the scene... Try using a lighter grey instead of pure white. That gives you room to increase the exposure a bit, until the snow looks white-ish again, which in turn helps with lighting the darker trees a bit more. Same with the clouds, give them a bit less albedo, so that you have room for increasing the exposure.
Regards,
Frank