INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 24: 591–601 (2004) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/joc.1014 SNOW COVER IN EASTERN EUROPE IN RELATION TO TEMPERATURE, PRECIPITATION AND CIRCULATION EWA BEDNORZ* Adam Mickiewicz University in Pozna´ n, Institute of Physical Geography and Environmental Planning, Department of Climatology, Pozna´ n, Poland Received 15 May 2003 Revised 12 December 2003 Accepted 12 December 2003 ABSTRACT The basic characteristics of snow cover occurrence in eastern Europe are described. For each month from October to May the range of ‘active’ snow-cover areas in Europe was determined. The boundary criterion for ‘active’ regions was adopted as snow-cover probability of between 10 and 90%. The correlation coefficients between the snow-cover characteristics (number of days with snow cover and its monthly mean depth) and other climatic variables (temperature and precipitation) were calculated. A strong positive correlation between the annual number of days with snow cover and the annual number of days with mean temperature <0 ° C was discovered for most parts of the study area. A negative correlation between the monthly number of days with snow cover and monthly mean temperature was found and its spatial distribution was analysed. A positive correlation between snow depth and precipitation appeared significant only in some areas. The influence of atmospheric circulation, expressed by North Atlantic oscillation (NAO) index values, on snow cover in the particular months was analysed. The correlation between the number of days with snow cover and the NAO index is large and statistically significant only in central Europe and it becomes insignificant to the east of 30 ° λ E. High values are noted only in the winter months. In autumn and spring, when the range of the ‘active’ areas moves to the east and the NAO becomes weak, the correlation is very small. Copyright  2004 Royal Meteorological Society. KEY WORDS: eastern Europe; snow cover; temperature; precipitation; NAO 1. INTRODUCTION The severity and snowiness of winters in Europe depend on the latitude and atmospheric circulation. Polar maritime air masses from over the Atlantic collide here with the Polar continental air masses connected with the Asian high. Thus, the probability of occurrence of days with snow cover (DSC) in Europe increases from 0% in the southwest up to 100% in the northeast. Frei (1997, cited in Clark et al. (1999)) has identified areas of ‘active’ snow-cover fluctuations in Eurasia as those areas where the probability of snow cover is between 10 and 90%. These areas cover more than half of Europe in the period of maximum snow cover extent (December–February (DJF)). Snow occurrence is an effect of the relationship between air temperature and precipitation. The temperature control is dominant in the transient snow regions where the mean winter temperature is slightly below zero and it often crosses the melting point. The situation is different in regions where the mean winter temperature is well below zero, where increases in snow depth are controlled mainly by precipitation (Clark et al., 1999). Hantel et al. (2000) have defined precisely the relationship between the mean temperature in Europe and the * Correspondence to: Ewa Bednorz, Instytut Geografii Fizycznej i Ksztaltowania ´ Srodowiska Przyrodniczego ul. Fredry 10, 61–701 Pozna´ n, Poland; e-mail: ewabedno@main.amu.edu.pl Copyright  2004 Royal Meteorological Society