The Role of Severe Thunderstorm Jetstreaks over North America on the Intensification of Atmospheric Rivers in the Euro-Atlantic

Recent case-study work has identified that jetstreaks induced by North American mesoscale convective systems amplify the downstream development of a Rossby wave packet (RWP). The misrepresentation of RWP amplification resulted in reduced forecast skill over the Euro-Atlantic in state-of-the-art global forecasting models several days later. The case-study coincided with a landfalling atmospheric river (AR) and its strength was observed to be modulated by upstream jetstreak magnitude in state-of-the-art forecasting models. Herein, it is hypothesized that the numerical misrepresentation of diabatically induced jetstreaks over North America could serve as a mechanism that deteriorates the forecast skill of Euro-Atlatnic ARs. The potential vorticity (PV) perspective is used to examine diabatic impacts on jetstream wind speeds. The manifestation of negative PV at upper-levels in the northern hemisphere has been shown to explicitly arise from convective air-masses. We design an algorithm that tracks closed contours of upper-level, negative PV air and composite instances in which the negative PV air is within close-proximity to ('interacts with') the jetstream. The dynamical impact of negative PV air advection on the jetstream as well its downstream response is facilitated through a lagged composite analysis. Quantifying the role of jetstreaks on downstream AR magnitude is facilitated through ensemble sensitivity analysis by using global ensemble forecast data. We discuss the implications of the results for forecasting ARs over the Euro-Atlantic.