The Onshore Surge of Marine Air into the Pacific Northwest: A Coastal Region of Complex Terrain

Abstract

Many coastal locations around the world experience rapid transitions from warm, dry continental air to cool, moist marine air. These onshore “pushes” or surges of marine air can be accompanied by strong winds, large temperature drops and a substantial increase in low clouds. A detailed case study of a typical Pacific Northwest event as well as a composite of several events are presented. It is shown that all major surges are initiated by synoptic-scale changes and that the mesoscale topography of the region “amplifies” the synoptic signal. Annual, monthly and diurnal climatologies are discussed. This paper also discusses the origin of associated West Coast phenomena such as heat troughs and narrow coastal pressure ridges.