The Pacific Northwest corner of the United States sees its share of rainy days. In fact, many people seem to think the rain never stops. They would be shocked to visit the Quinault Rain Forest on a summer day when it has not rained for three weeks and the mosses have shriveled into dormancy. Then again, a wet February day in the same spot would reveal just why a rain forest exists in this part of the world in the first place.
Weather on the Olympic Peninsula can be merciless, impossible to predict, and above all, intensely powerful. From the profusion of mushrooms in autumn forests to the glittering blue glaciers that top our mountains, every bit of Olympic National Park owes its existence to the workings of water and air in our atmosphere.
The Olympic Peninsula’s location greatly affects its weather. Though not connected to the nearby Cascade Mountains, we depend on them for protection from masses of cold Arctic air that come down from Canada. Most of that air stays on the east side of the Cascades, leaving us with mild temperatures moderated by the ocean. Winter days rarely get below freezing at sea level and summer daytime temperatures are usually 60-70° F (15-21° C). Even winter low temperatures in the mountains are seldom below 0° F (-18° C). The ocean is also the source of most of the Peninsula’s weather systems. Great storm clouds brimming with moisture move inland and run into the foothills of the Olympic Mountains. The mountains force clouds upward. As the air gets colder and air pressure decreases, these storm clouds cannot hold as much moisture and the water falls as rain in the lowlands and snow in the high country. The west side valleys in Olympic National Park are the wettest spots in the continental United States. The Hoh Rain Forest records an average of almost 12 feet of rain every year! Mount Olympus, the Peninsula’s highest point at 7,980 feet (2,432 meters), is estimated to get over 50 feet (18 meters) of snow!
On the other side of the mountains, storms continue their eastward journey. Though much of their precipitation has already fallen, more moisture is wrung out of the clouds as they move inland, blanketing Hurricane Ridge in an average of 30-35 feet (10 meters) of snow annually. The northeastern parts of the Olympic Peninsula lie in a dry rainshadow. The town of Sequim gets only 16 inches of rain a year. Farmers need to irrigate their fields and a few prickly pear cactus grow there, less than 35 miles from lush temperate rain forests!
The drastic contrast in precipitation promotes diverse habitats and wildlife across the landscape of Olympic National Park. Traveling from sea level to the mountains is like walking through a natural history museum––exhibits of varied plant communities are lined up side by side as you ascend. Mild temperatures and abundant rainfall nurture towering, record-sized conifers in westside forests. In the northeastern Olympics fire-adapted species like manzanita grow. While upslope the heavy snowpack feeds streams and shapes wildflower meadows throughout the year. Olympic National Park preserves evidence of water and wind, and the power those forces exert on anything they touch. Every time you explore tidepools, hike along a river or watch blazing wildflowers tremble in a mountain breeze, you are witness to that continuing power. Imagine what your grandchildren, and their grandchildren, might see if they came back to the very same spot many years and many storms from now.
The Hoh Rain Forest, even with 135 inches of yearly rainfall, experiences a summer drought: weeks can go by with no rain. Many of its plants, like the giant Sitka spruce, cannot live in a dry climate. How do they survive? A night on the west side will give you a clue. Fog often rolls in after sunset and may linger until late morning. Heavy fog can add more than 30 inches of moisture to the forest every year, nearly as much as Seattle receives in a year of rain. Plants can take that water right out of the air through their leaves. It also condenses, dribbles down tree trunks and drips off the ends of needles––so the forest sees rain even when none is falling!
The Pacific Northwest has a reputation for being dark and gloomy, shrouded in year-long mist. Indeed, the west side of the Olympic Peninsula is the wettest spot in the lower 48 states. But the dry eastern Olympics tell a different story. Much of the area's weather originates in the Pacific Ocean. Fronts storm inland from the southwest, heading straight for the Olympics. As the clouds rise over the mountains, pressure and temperature drop, so the air can no longer hold all its moisture. The moisture falls as rain and snow. By the time the clouds pass northeast of Mount Olympus and the Bailey Range, they have dropped most of their water. So here in the eastern Olympics, we are in a dry rainshadow. Just as less sunlight reaches the shadow of a tall building, less moisture reaches a mountain's rainshadow. The Hoh Rain Forest can get 140 inches of rain a year, but Sequim, just north of Deer Park, gets only 18 inches!