The meandering variability of upper-tropospheric jet streams have a strong influence on the surface weather of the middle latitudes, and very large meanders of the jet streams lead to extreme surface weather including heat waves, cold air outbreaks, and heavy precipitation. Classical linear wave theory can account for jet meanders but the theory assumes that the meanders have small amplitude, an unfortunate limitation since the meanders that matter for extreme weather are quite large. In earlier NSF-funded work the Principal Investigator (PI) pioneered a theory of wave dynamics which overcomes the small-amplitude constraint of linear theory and is thus better suited to real-world weather. The theory is based on a conserved quantity called Local Wave Activity (LWA), a measure of the waviness of the atmospheric circulation that can be used to identify the dynamical mechanisms responsible for important forms of wave behavior in the jet streams. Work performed here uses the LWA framework to address three longstanding problems in middle-latitude atmospheric circulation dynamics, the first of which is the suppression of cyclonic weather activity in the storm zones of the North Pacific and North Atlantic, which is typically weaker in midwinter than in October and March despite seemingly more favorable conditions for cyclogenesis. The work is guided by the hypothesis that the key issue is the exchange of LWA between weather systems and lower-frequency flow variations. The seco