How do we know when the Madden Julian Oscillation is actually impacting mid-latitude circulation?

While our knowledge pool continues to expand regarding the global-scale impacts of strong Madden Julian Oscillation (MJO) events, we still struggle as a community understanding the processes that often lead to these impacts. For example, forecasters too often overuse the MJO as a reason to explain why a particular state is being observed over a region solely based off the current and projected "phase" of an empirical orthogonal function (EOF) based MJO index without any physical explanation of why this state may be evolving. We often get consumed by the "black box" of the MJO phase space-diagram and simply just attribute causation rather than pin-point the underlying driving mechanism. So how can we tell if the MJO is actually playing a role on modulating extra-tropical circulation? What are tell-tale signatures that a forecaster can identify that shows the MJO is actually forcing a high-latitude response that can result in an arctic air mass intrusion over the U.S.? This study will aim to isolate key features that could bridge some of the gap between the tropical-extratropical climate interface.