why does it rain so much in washington

The Pacific Northwest is home to some of the most breathtaking scenery in the United States, but that greenery comes at a cost. It rains in the Pacific Northwest, and it rains a lot. Despite the gorgeous landscapes and cosmopolitan cities, the western parts of Washington and Oregon get a bad rap for how gray and dismal they can be. But why exactly does it rain so much in the Pacific Northwest? The reason gloomy weather is so common boils down to prevailing weather patterns and the unique terrain that makes this part of the world so gorgeous. This stretch of land between Portland, Oregon, and Seattle, Washington, usually finds itself directly under the track of the jet stream. The jet stream is a fast-moving river of air that encircles the Northern Hemisphere right around the latitude of the U. S. -Canadian border. Whenever the jet stream swoops to the south, creating a trough, it can generate low-pressure systems at the surface that produce heavy rain and high winds. These troughs and resulting low-pressure systems often intensify in the Gulf of Alaska and over the Pacific Ocean off the coast of Washington, allowing large storms to crash into the coast with ease. Most of these storms are run-of-the-mill rainmakers, lasting for a day or two before moving on, but some of them can be enormous and cause significant wind damage and flooding.


While the photogenic low-pressure systems that swirl into the coast are the driving force behind the Pacific Northwests seemingly endless rains, its the regions terrain that locks in those dismal weather conditions. When moist winds blow inland with an approaching storm, the high terrain of the Cascade Range forces the moist air to rise into the atmosphere, enhancing the thick clouds and steady rainfall. Even though it rains quite a bit along the northwestern coast, actual rainfall totals in the Pacific Northwest vary wildly from place to place due to changes in elevation. Some spots at high elevation right along the coast or along the Cascade Range can see more than 10 feet of precipitation in a single year, accounting for both rain and the equivalent amount of liquid in snowfall. Seattle, Washington, and Portland, Oregon, each only see around 36 inches of rain every year, which hardly makes these bustling metro areas the wettest in the country. Compare their rainfall totals to New York Citys Central Park, which measures nearly 50 inches of rain every year, and Mobile, Alabama, commonly one of the wettest cities in the United States; its proximity to the Gulf of Mexico gives it nearly 66 inches of rain every year.


The rain that does fall in Seattle and Portland, though, falls over a longer period of time. Between 1981 and 2010, both cities saw a little more than 150 days with measurable precipitation per year, compared to about 122 rainy days in New York City and just 115 in Mobile. This accounts for the Northwests reputation as the gloomiest part of the countrybut makes for spectacularly green landscapes when the skies clear out.
Most of Oregon isn't rainy at all, nor is is particularly cloudy. Even most of western Oregon isn't rainy or cloudy. What's really going on is that it happens to have less sunshine than most of the U. S. (which overall is a very sunny country), and Western Oregon and Washington have a lot of precipitation days. But even so, a hundred-odd days per year doesn't seem high to me, so it still is rather mysterious; however others must think otherwise. The fact that in a lot of the two states the rain is concentrated in the winter wet season may be another factor. There are a few exceptions to this debunking; the Cascades and parts of the immediate coastline, especially in Washington, do get plentiful rainfall, sometimes over 100 inches per year.


These places have less sun than most parts of the state (the only cloudy parts in my view) and more precipitation days that suggest rainy conditions. If you really want to see what abundant rainfall, moderately low sunshine hours, and a lot of precipitation days look like head to the Alaskan Panhandle. They have some genuinely rainy climates. Port Walter is the rainiest and averages over 200 inches of rain per year. Most of these places average over 150 precipitation days per year, some of them over 200 per year. Sun hours prevail in the mid 1000's annually, compared to closer to 2000 for western Oregon and Washington. Also compare that to the rest of the States, which are well into the 2000's or 3000's (the U. S. is a very sunny country overall). As for the relatively elevated rainfall, it comes from being closer to the mean storm track of (strong) storms that develop over the vast expanse of the Pacific Ocean. These storm systems have a long time to develop and are often laden with moisture. The upslope forcing over the Cascades also helps out in that particular area when it comes to rainfall/snowfall.

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