The Extended Period Precursory Signals of Strong Persistent Freezing Rain and Snow Events in Southwest China

Abstract In this study, daily temperature and precipitation data between 1950 and 2018 from 753 stations from National Meteorological Information Center, and NCEP/NCAR reanalysis data were used to screen freezing rain and snow events that occurred in the winters of 1951–2017 in southwest China (100°E–110°E, 22.5°N–32.5°N), in order to search for extended period warning signs of events. The combined anomalies index PCA ,established by the Mongolian Geopotential height pressure intensity, north–south position index and the southern trough intensity index, is closely related to the freezing rain and snow events in southwest China, and can be used as a link to explore the precursory signals of persistent freezing rain and snow events. The 1000-hPa height field of Iceland (60°N–80°N, 10°W–50°W), the North Atlantic (25°N–45°N; 20°W–60°W) and the Caspian Sea (30°N–50°N; 30°E–70°E) in the early mid-latitude was significantly correlated with PCA . The high disturbance signal in the upstream dispersed to the downstream 15–20 days in advance, which intensified the Mongolian high and deepened the southern trough. The combination anomaly of the Mongolian high and southern trough finally led to the strong persistent freezing rain and snow events in southwest China. The extended period forecast index of strong persistent freezing rain and snow events in southwest China was established according to the average geopotential height of key atmospheric regions 15 days ahead of the event. These findings provide a reference for the prediction of winter disaster events extension-period forecast in southern China.