Rain, Hail, Sleet, or Snow? Ask Mass.

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There is a popular saying that "everyone talks about the weather but no one does anything about it." Not true for UW atmospheric scientist Clifford F. Mass. Mass and colleagues have revolutionized weather forecasting in the Pacific Northwest, elucidating many of the processes and phenomena that have become the mainstays of our nightly television weather forecasts.

The UW atmospheric sciences department, the largest such academic program in the western U.S., is the West's "weather central." Many of the popular television forecasters in the Puget Sound area have received training in the department. UW faculty have worked over the years in close cooperation with the National Weather Service to study and improve the measurements and computer models used in weather forecasting for our region.

Analyzing the region's weather data with a fresh perspective, Mass and colleagues shed light on the causes of some of our weather patterns in the Northwest. In 1981, Mass first published his work on the Puget Sound Convergence Zone, a band of cloudiness and precipitation in northern and central Puget Sound formed when winds off the Pacific Ocean are split by the Olympic mountains, pass both to the north and south of that range, and then collide. The convergence zone creates large weather contrasts in Puget Sound, with warm temperatures and clear skies in the sections outside the zone, but low clouds, rain and cooler temperatures within it. Although the zone can occur at any time of year, it seems to have a yearly and a daily cycle. The convergence zone effect is most frequent during the late spring and early summer months, and during the afternoon and early evening.

By understanding the precise environmental conditions and factors that govern formation of the convergence zone, forecasters have been able to make more accurate and localized forecasts for our regions throughout the Pacific Northwest.

Other weather phenomena analyzed by Mass and colleagues include the severe windstorms that sometimes occur in the lee of the Cascade Mountains. Residents of Enumclaw, Washington, are not likely to forget such a windstorm over the holiday weekend of December 23-25, 1983, when powerful, gusty winds descended the foothills of the Cascades and wrought havoc in that area. Winds leveled buildings and barns, tore roofs off homes, and downed trees and powerlines. Damage due to that storm was estimated at $10 million. Winds were strongest downwind of gaps in the Cascade mountain range. An analysis by Mass and colleague Mark D. Albright suggests such storms are caused by a large pressure difference across the mountains coupled with an air mass that subsides over and to the lee of the Cascade crest. Detailed analysis of the event may allow forecasters in the future to predict such events more accurately, allowing residents time to "batten down the hatches."

Other studies have shed new light on why snowstorms over Puget Sound lowlands are so difficult to predict, and how they correlate with the El Nino pattern of warming out in the tropical eastern Pacific Ocean; why the characteristic daily variations in wind patterns occur; and what factors result in the surges onshore of cool, moist marine air following periods of warm, dry weather.

The researchers have used powerful computing technology to run computer models with a horizontal resolution of as small as three kilometers to simulate many of the local weather phenomena. Success with those simulations allowed them to take the next step and predict the weather in very high-resolution (27 km) forecasts. In that way, forecasts can be tailored for localized areas, such as the west slopes of the Cascades, the Seattle area, the east side of Lake Washington, and other local communities.

Mass's work has been aided by new data brought back from field experiments using radar-equipped airplanes--the craft used to fly into the eyes of hurricanes. And a new device called the wind profiler—a vertically-aimed radar instrument—at Sand Point Naval Air Station in Seattle allowed measurements of wind speed and direction to be made up to 3 miles above the earth's surface. Until the wind profiler was installed, there was no routine way to make measurements above ground level in the Puget Sound area.

Interested parties may access the high-resolution weather maps and other weather data on the World Wide Web over the computer Internet. Mass reports that some 51,000 "hits," or inquiries, have been logged between May and September of 1995--evidence of the facility's growing popularity among Internet users. The infomation may be accessed over the Web at: http://www.atmos.washington.edu/

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