SYNOPTIC CONDITIONS RELATED TO HEAVY SNOWFALLS IN TATRA MOUNTAINS

Synoptic patterns responsible for extreme snowfalls (exceeding 30 cm daily) in the Tatra Mountains were determined. Daily data of snow cover depth in six stations, regarding years 1991-2010, were used. The number of days with snowfalls did not reveal any particular trend in the last 20 years in the Tatra Mountains, apart from the highest elevation, where the seasonal number of days with snowfalls decreased significantly. Synoptic conditions of the abundant snowfalls were characterized using reanalysis data of daily sea level pressure, 500 hPa geopotential heights and grid-based temperature at isobaric level 850 hPa, derived from National Centers for Environmental Prediction (NCEP) - National Center for Atmospheric Research (NCAR) dataset. Four types of synoptic patterns favorable for heavy snowfalls in the Tatra Mountains were distinguished. Abundant snowfalls require sufficient supply of moisture at low temperature conditions. Cyclonal systems bringing snowfalls located over the central and eastern Europe, may form centers in the north and bring humid air masses from the the Baltic Sea region or in the south. In the latter case, distant humid and warm air masses from Mediterranean region transform on the long way and they meet the colder air coming by the lower stream usually from the closer distance from northern or eastern direction. The described processes signify warm fronts structure, with the active warm and humid air of distant southern origin climbing upwards on the cooler and more stabile polar air masses from the north or east. At the same time, blocking anticyclones spread over the Atlantic, suppressing western airflow, dominant in the moderate zone. The results obtained in the study could be useful for forecasting abundant snowfalls in the Tatra Mountains and for predicting the increasing risk of avalanches. Furthermore, they enable to evaluate and explain changes in the snowfall activity in the highest Carpathian range.