November 13, 2008
New book will tell much you didn’t know about Northwest weather
If you’ve ever wondered what the heck a convergence zone is, what a rain shadow is or just where the Seattle area ranks in terms of annual rainfall, you’ll find answers in a new book from a UW expert on Pacific Northwest weather.
The Weather of the Pacific Northwest explains many weather phenomena of Washington and Oregon, from snowstorms that hit only a tiny area to powerful windstorms that have ripped through the entire region.
“I wanted to create a very accessible book for the lay person, a fun book about the weather in the Pacific Northwest, one full of illustrations and photographs,” said author Cliff Mass, a UW professor of atmospheric sciences who has spent much of his career studying local weather and better ways of forecasting it.
“There’s a section on dust storms east of the Cascades, and even a chapter on UFOs,” Mass said. “The Northwest has wave clouds that look like UFOs, and in fact the whole UFO craze started here in the late 1940s when someone saw what looked like a UFO over Mount Rainier.”
What the person really saw, Mass said, was a lenticular cloud. Lenticular clouds, which are lens shaped, can stack up above mountains. In this case, such a cloud was mistaken for an alien spaceship.
The book, published this month by University of Washington Press, has sections about the mild winter temperatures of the so-called banana belt of southwest Oregon, winds in the Columbia Gorge, the region’s suitability for producing energy from wind and how to “read” the sky by identifying clouds.
It explains how, perhaps 25 times a year, an air mass is split by the Olympic Mountains, then reconnects over Puget Sound somewhere between north Seattle and Everett in what is called the Puget Sound convergence zone, an area that can be rainy even though the sun shines brightly just 15 miles to the south. It tells how the coastal mountains in Washington and Oregon create a “rain shadow,” wringing a great deal of moisture from Pacific storm systems on the west side of the mountains so substantially less moisture is left for areas east of the mountains. And it dispels the myth that the Seattle area is one of the rainiest places in the country, comparing Seattle’s annual rainfall of 37 inches with the averages of 47 inches in New York City and 56 inches in Miami.
The book also discusses how climate features such as El Niño and La Niña in the equatorial Pacific Ocean affect our weather, how the region is likely to fare with global warming, and the effects of technology on the accuracy of local forecasts in the Northwest.
Understanding how Northwest terrain affects local weather conditions has fostered great improvement in forecast accuracy, Mass said. The wide range of topographical features such as mountains and bodies of water means weather can vary greatly in small geographic areas.
“Great variability exists here, but that doesn’t mean the weather is hard to predict. In some ways the weather here is very predictable because of the mountains,” he said. “We’ve grown to understand a lot about local weather, and this book is my way of summarizing the new knowledge.”
He notes that the 1962 Columbus Day storm that ravaged western Oregon and Washington with winds as strong as a category 3 hurricane came as a great surprise. The vastly improved understanding of the region’s weather characteristics since the 1960s, along with new technologies such as high-resolution computer modeling, allowed forecasters to accurately predict, several days in advance, other big gales, such as the Inauguration Day storm of 1993.
“Decades of research on local weather, much of it done here at the UW, is the foundation for regional forecast improvements,” Mass said.
That research has allowed him to devise computerized models that can provide accurate forecasts at scales of just a few kilometers. Such capability could make it possible, for example, to accurately predict a storm like the one in December 1990 that dumped as much as a foot of snow on Seattle while communities 25 miles away saw nary a flake. That storm, which hit without warning in the early afternoon and virtually paralyzed the city, is just one memorable event described in the book.
“I included the intense storms that people like reading about,” Mass said. “But I also have described local weather curiosities that might surprise people.”