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Currently, due to the global climate change and increasing frequency of weather events focus is on prediction of climate extremes. Large-scale meteorological anomalies can cause long-term paralysis of social and economic infrastructure of the major mountain regions and even individual states. In winter periods, these anomalies are associated with prolonged heavy snowfalls and associated with them catastrophic avalanches which cause significant social and economic damage. The climate system maintains a certain momentum during periods of adjustment and transition to other conditions in the ratio of heat and moisture and contains a climate «signal» of the climates of the past and the future. In our view seasonal and yearly extremes perform the role of these indicators, study of which enables for a deeper understanding and appreciation of the real situation of the climate periods related to the modern ones. The paper provides an overview of the criteria for selection of extreme winters. Identification of extremely cold winters during the period of instrumental observation and assessment of their snowiness and avalanche activity done for the Elbrus region, which is a model site for study of the avalanche regime in the Central Caucasus. The studies aim to identify the extreme winters in the Greater Caucasus, assess their frequency of occurrence, characterize the scale and intensity of the avalanche formation. The data obtained can be used to identify winter-analogues in the reconstruction and long-term forecast of avalanches.

The paper deals with study of snowiness and estimation of modern tendencies of its changes in the area of Krasnaya Polyana in the West Caucasus. Olympic Games will take place here in February, 2014. The paper is based on the data of meteorological stations Krasnaya Polyana (567 m), Achishho (1880 m) and snow surveys along the Mzymta River valley (0–2500 m). Period under study characterized by winters with different snowiness. This difference is analyzed due to their changes in altitude levels. During two last decades, the noticeable reduction of snowiness occurred in the investigated district. The dependence between snowy winters and periods of cold temperatures is identified. In seasons of anomaly high and low snowiness the difference of snow depth can reach 5 m (Achishho). In places of Olympic ski lower stations (Gornaya Karussel, Gasprom, Rosa-Hutor) the temperature of cold period runs from −1,6 ºC up to 4,9 ºC, and the periodicity of winters with positive temperatures is 86% on this level. Parameters of winter conditions are given in the paper, and we can consider them as a paradox of Krasnaya Polyana winters

Definition of such phenomenon as “catastrophic avalanche” is presented in this arti-cle. Several situations with releases of catastrophic avalanches in mountains of Caucasus, Alps, and Central Asia are investigated. Materials of snow-avalanche ob-servations performed since 1960s at the Elbrus station of the Lomonosov Moscow State University (Central Caucasus) were used for this work. Complex-valued measures of engineering protection demonstrating different efficiencies are consid-ered.