Linking Stratospheric Polar Vortex Geometries with S2S Forecasting

Variability in high-latitude stratospheric flow, including major sudden stratospheric warming (SSW) or strong polar vortex events, can modulate the troposphere and have meteorological implications on surface conditions for up to 60 days. Extreme winter weather and cold air outbreaks associated with stratospheric variability have proven to be both a societal and economic issue for the United States. However, leveraging the potential window of opportunity for increased predictability of these extreme winter weather events during stratospheric variability is an open problem.

This research applies metrics of the stratospheric polar vortex geometry in assessing stratospheric variability and examines the potential usefulness of the geometry metrics in subseasonal-to-seasonal (S2S) forecasts of winter weather extremes. First, a cluster analysis of historic stratospheric vortex variability reveals the type of vortex variability associated with certain extreme weather outcomes for the U.S. Using the cluster analysis as a foundation, we consider the temporal evolution of the vortex geometry using a best-fit ellipse to describe the shape and location of stratospheric vortex as it transitions into the high-impact weather clusters, and the implications of that variability on impacts. We present the results in the context of building towards methodology to develop forecast tools and examine forecast bias in S2S forecasts of stratospheric impacts.