The Environmental Field and Ensemble Forecast Method for the Formation of Freezing Rain over Guizhou Province

During the winter storm, freezing rain is one of the most difficult to forecast among the various types of precipitation. The freezing rain over Guizhou and Hunan provinces is formed because of the interaction between the mid-higher latitude and the lower-latitude weather systems. The most important weather systems are the high-level subtropical jet stream front, the lower-level Yunnan-Guizhou quasi-stationary front, and the southwesterly jet. To accurately analyze the occurrence of freezing rain under these complex weather systems, we have proposed a new set of diagnostic method, which is a combination of the "dynamical factor" and the "three-step judge method." Meanwhile, we have applied the method to forecast freezing rain in Guizhou Province, China, where freezing rain occurs most frequently. We first used the dynamical factor vertical integral baroclinic vorticity parameter (q_Bsum) to find the possible weak rainfall region owing to atmospheric baroclinity, and then used single-station radiosonde data to employ the following three-step judge method. Finally, we determined the regions where freezing rain may occur in the future.