Synoptic reasons for heavy snowfalls in the Polish – German lowlands

Abstract

Daily circulation patterns responsible for heavy snowfalls in the Polish – German lowlands were analysed. Composite maps of sea level pressure (SLP) and 500 hPa geopotential height means and anomalies were constructed for the days with an increase in snow cover depth by ≥5 cm. Contour maps show negative anomalies of SLP and 500 hPa level over central Europe, indicating a low pressure system. Strong positive anomalies of SLP appear over Scandinavia and the northern Atlantic with the centre of positive anomalies located over Iceland. Weaker negative anomalies are observed in the Azores region. This confirms the strong negative correlation between snow cover appearance and the North Atlantic Oscillation index in Europe. The days with heavy snowfalls were clustered using the Ward’s method. Three types of circulation patterns were distinguished, each of them characterised by a low pressure system over central Europe. Type 3 represents the northern position of the low with its centre over the Baltic Sea, Type 2 shows the southern position of the low with its centre over the Adriatic and the Ionic Sea and Type 1 represents the low location between the two previous patterns with a wide meridional trough over the Atlantic.