The Remote Role of North-American Mesoscale Convective Systems on the Forecast of a Rossby Wave Packet: A Multi-Model Ensemble Case-Study

North American Mesoscale Convective Systems (MCSs) have been linked to instances of poorly forecasted Rossby wave packets (RWPs). A computationally inexpensive investigation is proposed to demonstrate a dynamical mechanism by which MCSs modify a RWP associated with a high-impact weather event. Global ensemble forecast data, reanalysis and high-resolution observations are used to assess the remote role of negative potential vorticity (PV) arising from divergent outflow on RWP propagation coinciding with the 11–21 June 2017 European heatwave. In this case, synoptic-scale bands of negative PV which advect toward the jet stream arise from regions of active MCSs. The forecast data results show that the numerical misrepresentation of the anticyclonic circulation associated with negative PV can impinge on the forecast of a RWP. In each of the four forecasting models assessed, ensemble members that advected lower values of PV toward the equatorward branch of a North American ridge favored enhanced poleward amplification of the ridge and a more eastward progression of the RWP. The more eastward displacement of the RWP also coincided with an enhanced wave activity flux downstream. Although, we do not find a significant impact on the forecasted heatwave. The results urge further investigation into the role of negative PV in remotely influencing high-impact weather.