Relationships between the Intensity of Cold-Air Outbreaks and the Evolution of Synoptic and Planetary-Scale Features over North America

Abstract

Much of the previous work on cold-air outbreaks has examined the synoptic development associated with small samples of strong outbreaks. In this study, a synoptic climatology of cold-air outbreaks is developed from a large outbreak sample displaying a wide range of intensities over the southeastern United States. Relationships are developed between the intensity of cold-air outbreaks and the magnitude of planetary- and synoptic-scale surface temperature, pressure, and 500-mb height anomalies over North America. These atmospheric fields are passed through a Gaussian nine-point filter in order to distinguish between planetary- and synoptic-scale features. Lag correlation fields are constructed to identify patterns in the strength of the relationship between the outbreak intensity and the magnitude of the planetary- and synoptic-scale atmospheric fields over North America during a 12-day window preceding the cold-air outbreak. Planetary-scale circulation anomalies are found to be more strongly related to the intensity of cold-air outbreaks than the synoptic-scale anomalies. Incipient outbreak intensity is most strongly related to persistent, positive surface pressure anomalies over western Canada 6?12 days before the outbreak. Several days before the outbreak onset, outbreak intensity is more strongly associated with negative 500-mb height and surface temperature anomalies over the Great Lakes and the Midwest, respectively.