Analysis of environment conditions of a sustained heavy rain event occurred in western Meiyu front and cause of extreme precipitation in Guiyang

Based on routine upper-air and surface observations, NCEP/FNL reanalysis data and TBB data from FY-2E satellite cloud images, we have investigated the meso-scale environmental field features of a sustained heavy rain event occurred in western Meiyu front in Guiyang from July 13 to 17 in 2014 and the cause of extreme precipitation in Guiyang, and then established the synoptic pattern of this event by the synergetic analysis of multi-element data. Results are as follows. (1) This event occurred in the background of a stable single blocking high type Meiyu. The severe precipitation continued for 3-4 days in Guizhou is caused by the mutual effect of shear line with low vortex in the mid- and low-level, low-level jet and the surface stationary front (Meiyu front). (2) The origination, maintenance and movement of rainband with Meiyu front cause the severe precipitation in the different regions of Guizhou. In terms of this event, the effect of rainband with Meiyu front on Guizhou can be divided into four stages, of which at the third stage the replacing, merging and slow moving of several β-mesoscale convective cloud clusters make precipitation in Guiyang and some surrounding counties exceed historical maximum during the slow southward movement of western Meiyu front. (3) The interaction between systems in the mid- and low-latitudes results in abnormal and strong water vapor transport. Super severe typhoon (No.1409) Rammasun entered the South China Sea on July 16, 2014 makes northerly water vapor transport in the western side of subtropical high intensify, and it converges southwest warm and wet airflow from the Bay of Bengal to Guizhou to form an intensive center of water vapor flux and vapor convergence, which is considered to be the major cause for the extreme precipitation in Guiyang. (4) Comparing to the other 4 heavy rainstorm events occurred in Guiyang between May and September from 2010 to 2014, the long duration of precipitation for this event may be another major cause for the extreme precipitation. (5) During the severe precipitation in Guiyang, the radar echo of severe precipitation is observed to be characterized by stratiform cloud mixed cumulus, low centroid and warm cloud precipitation. Meanwhile, strong southwest jet stream and mesoscale cyclonical convergence are evident in the radial velocity chart.