Differentiating Average and Extreme Extra‐Tropical Cyclones by Their Vertical Tilt and Potential Vorticity Structure

This study compares the vertical tilt and potential vorticity structure of average and extreme extra‐tropical cyclones (ETCs) in the Northern Hemisphere during the cold season (October–March) in ERA5 reanalysis. Vertical tilt is quantified using a novel two‐component (directional and lateral, aligned with and across cyclone motion) horizontal offset between the near‐surface and upper‐level ETC centers. Compared to average ETCs, extreme ETCs exhibit an amplified tilt magnitude during the intensification phase and a change in the sign of the lateral tilt prior to maximum intensity. Accounting for the tilted vertical structure, this study shows that average ETCs are associated with an upper‐level positive anomaly, which is constant through the ETC lifecycle, while the intensifies from the bottom up. In contrast, extreme ETCs are characterized by a growing magnitude of upper‐level anomaly, and a simultaneous intensification throughout the lower levels.