Macro- and Microphysical Properties of Atmospheric River Snowfall: Results from Two Instrument Sites

Abstract Atmospheric rivers (ARs) can produce intense snowfall events with different characteristics compared to snowfall events not associated with ARs. This study uses remotely sensed and in situ observations at multiyear instrument sites in Marquette, Michigan, and Hyytiälä, Finland, to comprehensively evaluate snowfall properties during ARs and compare them to snowfall properties during non-AR conditions (NoAR). A snowfall classification scheme is applied at each site to find deep (large scale) snowfall events and classify them as either AR or NoAR snowfall. To identify differences between the two regimes, reanalysis data products and ground-based observations are utilized to examine the large-scale properties, environmental conditions, and macro- and microphysical characteristics of AR and NoAR snowfall. During AR snowfall, there is a preferential large-scale setup at both instrument sites that results in enhanced water vapor transport. The AR snowfall events produce higher snowfall rates, as well as a higher number of denser and faster-falling snow particles compared to NoAR snowfall. Significance Statement In this study, we aim to better understand the physical properties of snowfall that are coincident with an atmospheric river. This is important because atmospheric rivers produce enhanced snowfall events in mid- and high-latitude regions whose snowfall properties are relatively understudied. We find that snowfall coincident with an atmospheric river is particularly intense and produces more, faster-falling, and heavier snow particles than snowfall not coincident with an atmospheric river. Our findings also suggest that different processes may be contributing to the intense nature of atmospheric river snowfall, which can be leveraged to better understand and predict these events.