Analysis of the long-lasting cryogenic freezing rain and snow weather in the beginning of 2008

From the forecasting perspective, main characteristics of the cryogenic freezing rain and snow weather in the beginning of 2008 as well as associated circulation features have been analyzed. Meanwhile, we also studied the causes for the freezing rain and snow storms. During this period, the atmospheric circulation patterns were stable. The polar vortex was strong and located in the northern part of the East Hemisphere. The cold air from polar areas and warm air from the tropical sea confronted each other for a long time, which was considered as the main reason for this event. The blocking high in the west of the Baikal was robust, and the low trough (vortex) in central and western Asia was vigorous but less versatile in its position. The southwesterly flows were persistent at 700 hPa and there were active shears and vortex activities at 850 hPa, which provided a very favorable condition for the low-level convergence necessary for the subsequent rainfall. In mid troposphere, vortex activities developed over the Tibetan Plateau with positive vorticity propagating eastward to the coastal regions of eastern China. The western Pacific subtropical high was intensive, stretching westward and northward. The subtropical frontal zone was puissant, and the northto south temperature gradient was large. The quasi stationary fronts in Huanan and Yunnan-Guizhou were maintained steadily. The warm air over the tropical sea was active. The stable inversion layer and the thicker melting layer were one of the main reasons for the longtime freezing rain. There were four episodes associated with this event. The first episode was resulted from the interaction between the cold and warm air. Later, the other episodes were caused by the quasi-stationary front in Huanan and YunnanGuizhou, as well as the dispersed from the north cold air. The main reason for the snow storms in the beginning of 2008 was that positive vorticity in the Sichuan Basin propagated eastwards to the coastal regions of eastern China. Abundant water vapor and intense upward motion were very favorable for the intense snowfall.