Do Rossby wave packet envelopes exhibit enhanced predictability?

Rossby wave packets (RWPs) organize large-scale energy transport in the atmosphere. The significance of this energy transport for atmospheric predictability and teleconnections has long been recognized. We here focus on RWPs along the midlatitude jet, which have received much attention as predictable precursors to high-impact weather events. More generally, these RWPs organize midlatitude weather systems and shape their climatological occurrence frequency and intensity. RWPs are frequently considered as physical entities identified by the Rossby-wave envelope. From this perspective, RWPs appear as features on a scale larger than that of the underlying troughs and ridges, i.e., they appear as features that live on scales larger than the synoptic scale. In particular, with resepct to predictability, a long-standing hypothesis by Lee and Held (1993) states that "the packet envelope should be more predictable than the individual weather systems, because the packet can remain coherent despite chaotic internal dynamics". Testing this hypothesis with ERA5 re-forecasts, we find that the RWP envelope does not exhibit this hypothesized higher predictability, at least when compared to the pattern of the underlying Rossby waves themselves, and until the end of the available lead time range of 10 days. This statistical result is substantiated by the examination of the underlying error-growth mechanisms. We will further provide a dynamics-based explanation of the counterintuitive result that the (seemingly) larger-scale envelope feature does not exhibit the expected higher predictability. Finally, we will conclude the presentation with a discussion of the role of the envelope perspective for predictability questions beyond the medium range.