The high pressure in the eastern Pacific tends to park itself off California all summer but is farther south off Mexico during the winter. Most directly ocean-influenced areas at 15-25 degrees latitude (Caribbean, northern Australia, etc.) have wet summer/dry winter climates, with weather systems usually moving from east to west. At 30-40 degrees latitude you get the wet winter/dry summer (so-called Mediterranean) climate, and weather nearly always moves west to east. Many places in the in-between 20-35 degree range can be dry most of the time, and nearly all the world's big deserts are in that range.
So the whole western US is in the latitude zone predisposed to wet winter/dry summer. The storm track from the NW that brings consistent winter snow reaches California in April only about half as frequently as in March, but it reaches the Wasatch about 3/4 as often. These storms are still nearly all snow because of their source. And we all remember these outlier storms from the NW that occasionally dump snow in May or even June.
Summer moisture generally comes from tropical Mexico. The southern 2/3 of Arizona and New Mexico get more precipitation in summer than winter. Some of this moisture gets up to Colorado and even Wyoming I've been told. But it would have to flow east to west to get into California, so our mountains are much drier than the Rockies in summer. From MarcC's description, the Wasatch are borderline. They get some of the summer moisture, but not as much as the Uintas or Colorado.
The Colorado mts are poorly understood.
By me too. They don't line up in a simple N/S line like the Sierra, Wasatch or Tetons. There are a bunch of little microclimates sensitive to the precise direction of storm tracks. From living there a lot, ChrisC has figured out how it works for Telluride.
By the time weather has worked its way through Colorado, there's nothing straightforward about it. I think the Gulf of Mexico is the major source of precipitation east of the Rockies, and that can't be a good thing for those of us who want more snow and less rain.
One virtue of Colorado is that the altitudes are so high that even a tropical storm from Mexico may end up as snow there. Gulf moisture off the plains is the reason for the big bump in April/May Front Range snowfall. And October snow at Wolf Creek is usually the end of a tropical storm. The early December dump that set up this year's banner SW season came from Mexico and thus was high water content and gave those areas a much better than normal early season base.
