Northern Pacific sea-level pressure controls rain-on-snow in North America

Rain-on-snow (ROS) events, a phenomenon of liquid rainfall falling over accumulated snowpack, cause quick melting of snow, often leading to rapid and catastrophic flooding. Here we explore the causal drivers of ROS events across North America. A ROS identification method is proposed, which builds on the existing methods but adds more realism in terms of rain and snow conditions for ROS occurrence. We consider a wide range of observed hydrometeorological variables along with climatic oscillations over the period of 1951 to 2022. Causal linkages between the potential drivers and ROS frequency are explored by implementing Convergent Cross Mapping (CCM). Results suggest a strong causal link between the North-Pacific (NP) Index, a measure of sea-level pressure in the Northern Pacific Ocean, and ROS frequencies in North America, specifically in the eastern and western parts. We show the association of the NP index with the hydroclimatic variables and explain how this association might have contributed to this causal link. Thus, our findings provide valuable insights into the potential mechanisms of ROS events in different regions in North America.