workingtorv,
The thing about the weather in the western half of the USA is that the altitude is a major factor, unlike most of eastern North America. I grew up on the east coast of the US but have been in California for 10+ years and it's really a different mindset regarding the weather. For example, if you're in Ottowa and it's below freezing and snowing then it's probably below freezing and snowing in Quebec and probably the same in Toronto (generally speaking). But out here it can be sunny and mild in one area but an hour away it's freezing and snowing. And it's largely because of the altitude, and can be as large as an entire state, as one poster said, Wyoming, along I 80 is 6000-7000 feet for most of the state, or it can be a small as one mountain, such as Big Bear mountain here in S California, which can, and does, get many feet of snow, at 6500 feet elevation. But drive to where I live and it will be 30-40 degrees warmer. So my advice is to know the areas that are mountainous, such as the places already mentioned, and also be prepared for a layover in case of unexpected weather.
Bob