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 long simulation made with the HARMONIE-Climate convection-permitting regional climate model applied at 3 km resolution. Snowband days are identified using a set of previously established criteria describing environmental conditions favorable for sea-effect snowfall, combined with an additional threshold on snowfall flux. Snowband days occur most frequently (up to a few days per year in a 3km×3km 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 the majority of the northern Baltic Sea, snowbands occur typically between November and February. Winds with an easterly component at the 900 hPa level 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 and March. This study provides useful context for operational forecasters and forms the basis for future research on how the occurrence of these events may change in a changing climate.