I would have left in early summer

The winter of 1846-47 was a particularly bad winter. From what I understand the Party reached the Truckee/Donner Lake area in November. November in the Sierras is normally hit and miss when it comes to snow at lower elevations. Basically they did reach the Sierra soon enough to cross safely without being effected by the winter in a normal year; considering they had just endured the deserts in the Great Basin, they weren't wanting to take any longer sitting through the winter. That said, what makes Donner Pass one of the snowiest places on earth is its propensity to get pounded by unrelenting Pacific Storms that dump epic snow on the area on a consistant basis well into April. That's pretty much what happend during the winter of 1846-47. If the Donner Party had crossed the year before or the year after, they likely would have made it with little issue at all.



"Let's get out of here before one of those things kills Guy!"

They did leave early enough, more than early enough. But then they listened to fools and made some bad decisions along the way. Then they still would have made it, but the first storm of the year came a month earlier than usual. Thanksgiving week is more typical time for the first snowstorm. I'm sitting here in January 2012, I'm 20 miles away from Donner Lake and it still hasn't snowed.

Bad decisions combined with bad luck, that's what gets ya.

In addition to what other folks have said, if memory serves (based on recently watching a Donner Party documentary), it took them much longer to get across the Utah desert than they had anticipated...weeks longer in fact. Combine that with a horrible winter storm that arrives a month earlier than normal, and I'd say you have a recipe for disaster.