陕西东南部一次伴有雷暴的暴雪天气分析

利用常规观测、多普勒天气雷达和ERA—Interim再分析资料(0.25°×0.25°),对2016年11月22日陕西东南部地区一次伴有雷暴的暴雪天气过程进行诊断分析。结果表明:(1)此次暴雪是在低层东路回流冷空气与中层暖湿气流共同作用下形成的,700 hPa存在强的风向风速辐合,辐合区前部16 m/s的西南急流,为暴雪产生提供了有利的动力和水汽条件。急流加强是降雪增幅的主要原因。(2)冷季、强的锋区和低空急流、冷垫、逆温层、锋区之上湿的中性到条件不稳定层结、强切变低CAPE、雷达带状回波是此类天气预报中需要关注的特征。(3)整体层状云降水中,局地对流性云团旺盛发展,是此次暴雪的云系特征,暴雪发生在对流云团加强西伸、移速减缓的时段;与本地暖季相比,暴雪对流云团的面积较小,最大反射率因子所在的高度较高。(4)由动力锋生产生的次级环流上升支促使冷垫之上的暖湿气流快速上升,触发条件对称不稳定能量释放,使气块在逆温层之上获得正浮力,是暴雪发生并伴有雷暴的主要物理机制。

Analysis on a Snowstorm Weather with Thunderstorm in Southeast Shaanxi

Using routine upper-air and surface observations, doppler weather radar and ERA- Interim reanalysis data (0.25°×0.25°), a snowstorm weather with thunderstorms in Southeast Shaanxi on November 22, 2016 is analyzed. Results showed that: (1) The snowstorm is occurred under the combination of lower level east backflow and middle level warm air. 700 hPa have strong wind direction and speed convergence in snowstorm area, 16 m/s southwest jet at the front of convergence zone, which provide driving force and water vapor, and also a major reason for the enhancement of Blizzard.(2) Some characteristics need special attention in the forecast of this kind weather, including cold season, strong front area and low level jet, low level cold air, inversion layer, wet neutral to conditional unstable layer, high shear low CAPE and band shape radar echo. (3)In the overall stratiform cloud precipitation, local convective clouds vigorous development. Blizzard took place during the convective cloud cluster westward extension and slowed down. Compared with the warm season, snowstorm convective cloud area is smaller and the height of maximum reflectivity factor is higher. (4)The up flow of secondary circulation forced by frontogenesis makes warm air over the cold air cushion raised rapidly, which triggered condition symmetry instability energy release and air parcel above the inversion layer obtain positive buoyancy is the main physical mechanism of snowstorm accompanied thunderstorm.