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The high-impact sea-effect snowstorm of February 2020 over the southern Black Sea

Demirtaş Meral

Acta Geophysica

2023

Vol. 71, no. 3

1361--1371

The early February 2020 wintry weather set in across the southern Black Sea and northern coastal region of Turkey. During the high-impact snowstorm event, northerly winds carried cold arctic air across the relatively warmer Black Sea, which caused intense sea-effect snow showers. The omega-block pattern was present on successive days. Atmospheric blocking analysis was conducted with an objective two-dimensional index. Blocking analysis indicated that it was related to quasi-stationary the north-eastern Atlantic ridge, which was the most favourable position for leading to cold spells over the Black Sea, because it enabled a prominent downstream trough there. Key factors conducive to sea-effect snowfall over the southern Black Sea were noted highlight for this weather phenomenon: (i) an upper-tropospheric trough—which carried warm and moist air masses from the Black Sea towards the lands; (ii) a prolonged ridge in the upper troposphere—which was associated with a blocking anticyclone at the surface; (iii) directional wind shear was less than 60° at the boundary layer; (iv) low-level winds were approximately 10–15 ms−1 and suitable wind direction; (v) temperature differences between the sea surface and the 850-hPa level were higher than critical limit of 13 °C; (vi) the ratio between the average low-level wind and the fetch was 0.033, which was good enough for cloud formation. Main findings indicated that the dynamical factors and meso-scale ingredients triggering and maintaining this sea-effect snowstorm were satisfactory, and they were essential to pinpoint the underlying factors of high-impact sea-effect snowfall.