I would suggest the afternoon time - when we did this, the morning folks had a lot of fog and even snow - couldn't see a whole lot. By the time we left at 1:00, the day was sunny and clear. I would suggest you avoid the car behind the engine - and if you do the round-trip - the last car. You get the smoke from the diesel engine. It was a spectacular, fun ride. We saw lots of eagles and Dall sheep.