Freezing precipitation in Russia and the Ukraine

Abstract. Conditions for freezing precipitation (FP), including freezing rain (FR) and freezing drizzle (FZ) for 8 airports in Russia and 4 in the Ukraine are studied on the basis of 10 to 20-year series of surface observations, radiosonde and objective analysis data. Statistical characteristics are presented of the FP episode durations and of occurrence frequency dependences on surface air temperature, wind direction and speed and cloud base height. From the radiosonde data, it is found that the "classical mechanism" of FP generation (for which, stratification of "warm nose" type in the cloud layer is necessary) is not frequent: most of FP cases are associated with "all cold" conditions in the lower 3-km layer, that is, with negative temperatures in and below the clouds.