Snowstorms over the Puget Sound Lowlands

Garth K. Ferber National Weather Service, Seattle, Washington

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Clifford F. Mass Department of Atmospheric Sciences, University of Washington, Seattle, Washington

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Gary M. Lackmann Department of Atmospheric Sciences, University of Washington, Seattle, Washington

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Michael W. Patnoe Department of Atmospheric Sciences, University of Washington, Seattle, Washington

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Abstract

Snowfall over the Puget Sound lowlands is the product of complex interactions between the synoptic-scale flow and the mesoscale topography of the region. Although heavy snowfall is relatively infrequent in this region, when it does occur it severely impacts transportation and commerce. The typical synoptic evolution of such snowstorms is characterized by high-amplitude middle- and upper-tropospheric ridging over the northeast Pacific Ocean and the passage and/or development of a short-wave trough over the northwest. United States and southwest Canada. At the surface there is an intense arctic anticyclone over the interior of British Columbia and a coastal trough (and often coastal cyclogenesis) along the British Columbia and Washington coasts. Significant snowfall can also accompany the overrunning of entrenched arctic air by the southwesterly flow in advance of an approaching Pacific cyclone or the passage of a low center to the immediate south of the region during periods of marginal temperatures, with snow falling in zones of heavier precipitation. A variety of mesoscale and regional aspects of Puget Sound snowstorms are described including arctic fronts, coastal troughing and cyclogenesis, and additional mesoscale topographic effects. There is a strong correlation between El Ni˜o/Southern Oscillation and snowfall over Puget Sound, with lesser (greater) snow amounts during El Ni˜o (La Ni˜a) Years.

Abstract

Snowfall over the Puget Sound lowlands is the product of complex interactions between the synoptic-scale flow and the mesoscale topography of the region. Although heavy snowfall is relatively infrequent in this region, when it does occur it severely impacts transportation and commerce. The typical synoptic evolution of such snowstorms is characterized by high-amplitude middle- and upper-tropospheric ridging over the northeast Pacific Ocean and the passage and/or development of a short-wave trough over the northwest. United States and southwest Canada. At the surface there is an intense arctic anticyclone over the interior of British Columbia and a coastal trough (and often coastal cyclogenesis) along the British Columbia and Washington coasts. Significant snowfall can also accompany the overrunning of entrenched arctic air by the southwesterly flow in advance of an approaching Pacific cyclone or the passage of a low center to the immediate south of the region during periods of marginal temperatures, with snow falling in zones of heavier precipitation. A variety of mesoscale and regional aspects of Puget Sound snowstorms are described including arctic fronts, coastal troughing and cyclogenesis, and additional mesoscale topographic effects. There is a strong correlation between El Ni˜o/Southern Oscillation and snowfall over Puget Sound, with lesser (greater) snow amounts during El Ni˜o (La Ni˜a) Years.

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