CPP-10. Meteorological Drivers of Arctic Rain-on-Snow Events and How Climate Change May Influence Associated Risks

Much of what is known about Arctic climate and weather patterns is changing due to anthropogenic warming. Warming may lead to both altered occurrences and strengthening of extreme events. Arctic rain-on-snow (ROS) events are of particular interest, in this regard. ROS events generate hazards in the transportation sector, ranging from flooding to icing and closure of airports. They can severely damage infrastructure, such as through slush avalanches. In the ecological sector, ROS events and subsequent icing impacts hooved animal species’ ability to forage – animals that are heavily relied upon by Indigenous Peoples. Ice growth resulting from ROS blocks access to food sources, sometimes leading to mass starvation events. This presentation focuses on ongoing research efforts to improve our understanding of the meteorological setup of Arctic ROS events. The analysis centers on a series of case studies, using output from ERA5 atmospheric reanalysis, station observations, and atmospheric soundings. Each of these events resulted in significant ROS impacts or confirmed ROS conditions. From a synoptic scale standpoint, blocking patterns play leading roles in the initiation of ROS conditions over an area, with atmospheric rivers also providing both direct and indirect influences. Features like low-level jets and resultant “warm noses” of higher temperatures and moisture transport represent other key meteorological components for ROS initiation. This presentation includes discussions on how climate change may alter the severity and frequency of Arctic ROS events, drawing on improved knowledge of the weather patterns leading to ROS conditions. While it is reasonable to expect that ROS events – which most commonly occur in the shoulder seasons of fall and spring – may increasingly be seen in midwinter, changes in ROS occurrence and their effects must also consider expected shortening of the snow-covered season, possible changes in blocking frequency, and wider and longer atmospheric rivers exhibiting even more moisture transport.