Sea-effect snowfall in the Baltic Sea area in 1998–2018 derived from convection-permitting climate model data

Abstract. Sea-effect snowfall forms frequently over the Baltic Sea in northern Europe. In its bordering countries, large snow accumulations and poor visibility associated with these, often intense, convective snowbands have had considerable impacts on society. This study presents, for the first time, the occurrence of snowband days over the full Baltic Sea area on climatological time scales. The climatology is investigated using a 21-year simulation made with the HARMONIE-Climate convection-permitting regional climate model applied at 3 km resolution. Snowband days occur most frequently (up to a few days per year in a 3 km x 3 km area) over specific regions of the Baltic Sea: near the eastern coast of Sweden, over the Gulf of Finland and the Northern Baltic Proper. Over majority of the northern Baltic Sea, snowbands occur typically between November–February. Winds with an easterly component favour the occurrence of snowbands along the eastern coast of Sweden and southern coast of Finland, whereas few cases in those regions occur with westerly winds. In addition, snowband days occur over the southern Baltic Sea, where the formation of snowbands is favoured by low-level winds having a northerly component and typically between December–March. This study supports operational forecasting of snowbands events and forms the basis for future research on how the occurrence of these events may change in a changing climate.