Freezing rain is a kind of rain that falls in liquid form but freezes and forms a coating of ice on the ground and on exposed objects. It is a high-impact disastrous weather in winter season (Fig. 1). China is one of the countries that experienced severe freezing precipitation, and nearly 84% of total freezing rain days in China occurs over Guizhou province.  

Fig. 1  The impact of freezing rain. (photo from China.com news on 5 Jan 2011)

By the joint efforts of DENG Difei and GAO Shouting from the Institute of Atmospheric Physics and the weather forecasters of Guizhou province, it is found Guizhou province is a favorable place for the interaction of cold air and warm air, because the cold air from the north and the warm air from the south can climb along the ladder-shaped eastern Yunnan-Guizhou plateau and converge over Guizhou province. Thus, a long-lasting local front called Yunan-Guizhou quasi-stationary front usually forms in winter. The mid-lower stratiform clouds near the front offers a suitable environment for the production of super-cool raindrops. Unlike the classic microphysical processes of "melting process" and "super-cool warm rain process" with the soundings to be entirely subfreezing, the freezing rain over Guizhou can also be developed via super-cool warm rain process with a warm layer (> 0°C) present (Fig. 2).  

Statistical study demonstrates the distribution of the number of days with freezing rain is highly correlated to Guizhou topography (Fig. 3). The unique topography of Guizhou including its elevation and distribution contributes to the highest frequency of freezing rain in China. Terrain sensitivity analysis also shows, regardless of an increase or decrease in the ladder-shaped topography over Guizhou, the statistical 27 °N band of the highest frequency freezing rain is eliminated.