The possibility of assessing the avalanche hazard in the North Caucasus mountains with the use of the data of modern Era-Interim, SCSR, and NCEP-NCAR reanalyses is considered. The data have been previously compared with the materials of weather stations (average seasonal values of the surface temperature and precipitation). The avalanche hazard was estimated with the use of a correlation matrix, which is based on a relationship between the avalanche hazard characteristic and the standard deviations of the seasonal values of temperature and precipitation. The synoptic processes that increase the probability of catastrophic avalanches were identified. The anomalously high avalanche hazard was shown to form at a negative anomaly of air temperature at land surface and in higher air layers at an integral moisture content of the atmosphere close to the norm.

The possibility of using the data of modern ERA-Interim, CFSR and NCEP-NCAR re-analyses to assess an avalanche danger in the mountains of the North Caucasus is considered. Previously, the mean seasonal values of the surface air temperature and seasonal precipitation amounts obtained from the reanalysis archives were compared with the data of meteorological stations. The mean temperature of the cold period (November-March) was best reproduced by the ERA-Interim reanalysis: the correlation coefficients amounted to 0.8-0.9, and the average deviation from the station data +/- 1.7 degrees C. The accuracy of measurements of precipitation is lower, but the magnitude of the errors does not exceed the limits of inter-seasonal variability. To estimate the avalanche hazard, a correlation matrix was used based on the relationship of the avalanche hazard indicator with the standard deviations of seasonal values of temperature and precipitation. The ERA-Interim reanalysis reproduces the avalanche danger in the North Caucasus most adequately (71% of coincidences with the actually observed events). Synoptic processes which may promote formation of catastrophic avalanches in the North Caucasus were also determined. The most typical situation is the position of a high-level cyclone over the Eastern Europe, accompanied by the invasion of cold air masses from Scandinavia that activates cyclogenesis in the Mediterranean. It was found that the extreme avalanche hazards occurred at negative anomalies of mean seasonal air temperature near the ground and in the middle troposphere (about 1.5-2 degrees C) when the integral water content of the atmosphere was close to the norm.

This investigation has been carried out to identify winters with the maximum frequency of avalanches in the Greater Caucasus. The analysis was performed for decades and for the entire period of instrumental observations (1968-2016). We chose severe snow winters which were followed by releases of particularly large and heavy avalanches (L-ma(x)) and the maximum area of damage to the mountain territory during the study period. The following materials were used for this work: 1) 47-year-old (1968-2016) series of data on snow avalanches from observations performed at the high-altitude station of the Faculty of Geography of the Lomonosov Moscow State University in the near-Elbrus area (Central Caucasus); 2) the results of winter and summer investigations of snow and avalanches in Arkhyz (the Western Caucasus); 3) materials of field works carried out in the Caucasus at different times; 4) the results of winter typing from data of 41 mid- and high-mountain meteorological stations in the Greater Caucasus; 5) literature sources; 6) survey data. The dependence of avalanche activity on the types of winters was established for key observational sites in the near-Elbrus area (Central Caucasus) and Arkhyz (Western Caucasus). This dependence formed the basis for determining the L-ma(x) winters from factors of the avalanche formation, i.e. the air temperature and precipitation for the cold period from meteorological observations. Based on the method of winter typing, the winters of the maximal avalanche occurrence were estimated from data of 41 meteorological stations of the Greater Caucasus for 1936-2016. Results of the typing revealed similar avalanche extremes as it was found from direct observations of releases of snow avalanches: on the Southern macro-slope of the Western and Central Caucasus - 1986/87; on the Eastern Caucasus - 1971/72. Two seasons, claiming the role of the L-ma(x) - 1967/68 and 1975/76, were revealed on the Northern macro-slope.

The climate change during cold seasons of 1995–2017 in the Central Caucasus is estimated, and its influence on the avalanche regime is shown. Data on the avalanche releases in the Central Caucasus for the period 1968– 2017 together with observations of high-altitude meteorological stations were used for the analysis. The paper presents estimates of snowiness of the winters and their frequency of occurrence in the area under investigation. The winter snowiness was noted to decrease since the beginning of the 2000s. The last decade of the period was not snowy, especially its series of six winters having very small amounts of snow. It is shown that in the second half of the XX century the heaviest snowfalls took place mostly in Januaries, and they were followed by releases of avalanches with the volumes exceeding 1 million cubic metres. In the early 2000‑ies, intensive January snowfalls were observed later, i.e. during the winter-spring period. In the warmer months March and April, the destructive potential of avalanches was noticeably smaller. In the present time, the warming and decrease of winter snowiness resulted in significant diminution of the avalanche hazard in the region. At the same time, on the background of general warming the certain increase in inter-seasonal variability of air temperature was noted. These changes may be compared to the warming of 1910–1945 when during its warmest phase the Europe suffered with one of the harshest winters in 1941/42. The swing of the «temperature pendulum» indicates that a harsh winter with heavy snowfalls and avalanches with catastrophic consequences may occur on the background of winters with mild and moderate avalanche danger. This is one of probable scenarios in the development of avalanche activity in the Greater Caucasus in the context of the current climate change.

В 1999 -2008 гг. выполнены исследования снежного покрова и лавин на северном склоне хр. Аибга, на высо- тах 800 -2200 м. Выявлены особенности метаморфизма снега и проведено картографирование лавин разных генетических типов. Выделены четыре типа снежной толщи с неустойчивыми структурными характеристи- ками, которые обусловлены: интенсивными снегопадами и преобладанием деструктивного метаморфизма (1); формированием под воздействие метелей снежных досок, лежащих на ослабленных горизонтах, на стадии конструктивного метаморфизма (2); накоплением большого количества мокрого снега и регрессивным мета- морфизмом (3); образованием сложно стратифицированной толщи снега, ледяных корок и горизонтов раз- рыхления (4). От гребня хр. Аибга лавины отрываются в результате обрушения снежных карнизов толщиной 10 -12 м и останавливаются в днищах каров, что увеличивает толщину лежащего там снега и создаёт угрозу ещё б льших по объёму лавин. Влажные весенние лавины способствуют формированию селей снеготаяния.

Для равнинной части региона выявлены асинхронность многолетнего хода снезапасов и зимней температуры воздуха и несовпадение экстремальных сочетаний аномалий параметров; для Хибин проведена типизация зим по лавинной опасности.