Moisture from the Pacific Ocean streams onshore in the form of clouds and humid air. It passes through the gap between the Sierra and Cascades and into the Snake River Plain where it is channeled through most of the Rocky Mountains with no high plateaus or mountain ranges to impede its progress.[1] It finally encounters upslope conditions at the head of the Snake River Valley at Ashton, Idaho; at Island Park, Idaho; at the Teton Range east of Driggs, Idaho; and at the Yellowstone Plateau of Yellowstone National Park where the channeled moisture precipitates out as rain and snow.[2] The result is a localized climate on the eastern side of the Rockies that is akin to a climate on the west slope of the Cascades or the northern Sierra. The head of the Snake River Valley, the Tetons, and the Yellowstone Plateau receive much more precipitation than other areas of the region, and the area is known for being wet, green, having many streams, and having abundant snow in winter.