Snow cover in western Poland and macro‐scale circulation conditions

Abstract The aim of the study was to find out the connection between the nature of winters in the western part of Poland (excluding the Sudety mountains) and the fluctuation in the atmospheric circulation in the North Atlantic region determined by the North Atlantic Oscillation (NAO) index. An attempt was made to establish the correlation between the NAO index and specific meteorological parameters in Poznań. The strongest positive correlation was obtained for the mean winter temperature (December–March) and strong negative correlation was found for the number of days with snow cover. Winter precipitation in Poznań was least associated with the NAO. The correlation coefficient was small and not significant. In the next stage of the study, the area of western Poland was examined; however, only one parameter, i.e. the number of days with snow cover, was taken into consideration. At each of 29 stations distributed in the study area the number of days with snow cover was proved to be strongly negatively correlated with the NAO index. Finally, the frequency of air flow directions was taken into consideration and their association with the NAO was examined. A strong negative correlation was obtained for the frequency of northeasterly and easterly air flow directions and a strong positive correlation was calculated for the frequency of westerly and northwesterly airflow directions. Such findings are consistent with the westerly flow of air masses during the positive phase and with the northerly and easterly flows during the negative phase. The results lead to the conclusion that the positive phase of the NAO causes mild and less snowy winters, whereas the negative phase increases the probability of severe and snowy winters in western Poland. Copyright © 2002 Royal Meteorological Society.