Just back from 5 days hiking in the North Cascades where we witnessed the rain shadow effect in, well, full effect. In Biology last week, we’d been discussing this phenomenon and how it leads to sharp differences in vegetation on either side of a mountain range. In our corner of the world, warm, wet air coming off of the Pacific Ocean slams into the wall of granite that makes up the Cascades and then has nowhere to go but up. As the air rises, it cools, causing the water vapor contained within it to condense, forming clouds that eventually release rain or snow. The forests and alpine meadows on the windward side of mountain ranges typically get pretty wet. When the air mass finally makes it over the hill, it doesn’t contain much moisture; ecological communities in the lee of the mountains are made up of plants and animals that can handle a life with little water. At home, the San Juan Islands sit in the lee of the Olympic Mountains and it’s the reason we typically get about thirty fewer rainy days each year than Seattle. This year, we just happened to be moving in to the mountains accompanied by an early autumn weather system.
Ducking out of the pouring rain to pick up our backcountry permits at the National Park Service Ranger Station in Marblemount, we were all pretty apprehensive about the coming week. Luckily, out of the eight groups of students, teachers and parents setting out into the hills, only one got seriously wet. The reason? Most of us started our treks east of the highest peaks. Although we were threatened by towering cloud forms, the rain shadow effect kept us (mostly) in bright sunshine and almost entirely dry.
Hiking west over Twisp Pass, my group was treated to thickets of fire engine-red huckleberry bushes. They still bore some perfectly ripened fruit after a summer’s worth of sunshine on the south facing slopes. The berries served as a welcome reward for a daylong climb from the valley floor up to 6700 ft. Crossing over the crest to the windward slope, the huckleberries disappeared and the denser, moss-covered forest muffled our steps and absorbed our voices. We paused one at a time to examine some of the crazier shapes and colors of mushroom growing there. Camping for the night alongside Dagger Lake, we woke the next morning to the drop in temperature following the wet weather and, far more excitingly, the product of cooling air and condensing water vapor at high elevations: snow!