Synoptic conditions of heavy snowfalls in Europe

Synoptic conditions of heavy snowfalls at four stations in Europe (Oslo, Bremen, Smolensk and Budapest) were analyzed using daily data of snow cover depth from 50 winter seasons (1960/1961–2009/2010). Composite maps of the sea level pressure and 500 hPa geopotential height means and anomalies were presented for the days with an increase in snow depth by ≥10 cm, for each station separately. In the same way, maps were presented for the 850 hPa temperature and the precipitable water content. Additionally, 48 h back trajectories of air masses for the chosen days with the highest amount of snowfall were constructed, using the NOAA HYSPLIT model. Negative anomalies of sea level pressure and 500 hPa heights, which correspond to low‐pressure systems spreading over Europe, are prerequisites for the occurrence of heavy snowfalls at each analyzed location. In Budapest, heavy snowfalls appear as a result of cyclonic cold fronts from the Mediterranean Sea. Another typical location of snow‐bringing low‐pressure systems is the Baltic Sea region. Negative pressure anomalies over the North Atlantic with a low‐pressure centre over the Norwegian Sea cause snowfalls in Oslo. There are two main sources of air masses bringing abundant snowfalls in Europe: the Atlantic region and Mediterranean. According to back trajectories, the humid air masses are transported over long distances and on the way they are shifted from the low troposphere in the source regions to the upper layers.