More on the Subseasonal Variability of U.S. Severe Weather Activity

Connecting severe storm activity to climate drivers on the subseasonal (30-60 day) time scale is an emerging field. For example, it is now known that the Madden-Julian Oscillation (MJO), which is a major mode of atmospheric variability on the subseasonal time scale, modifies Rossby wave activity over North America. This modified wave activity then affects severe storm activity by modifying storm environments on the synoptic scale, particularly from April to June. However, there are still many aspects of this relationship that are unknown, and those aspects were the subject of this research. For example, how do the intensity and location of the convective heating anomalies associated with the MJO (often referred to as its amplitude and phase) affect both the timing and placement of ridge-trough systems over North America? Furthermore, is there seasonality to that relationship, and does it depend on the antecedent atmospheric state already in place across the northern Pacific Ocean or North America? Finally, there exist several metrics by which to quantify the MJO state; does one of them better describe the MJO-severe activity relationship than the others, and is there any difference between tornado and hail activity? These aspects of subseasonal severe weather variability were explored in this study.