基于两次副高边缘川西暴雨的预报思考

对于发生在副高边缘的川西暴雨,由于开始期影响系统不明显,暴雨云团完全由盆地内部自身生成并发展,预报难度较大。利用过程开始前能够获得的常规观测资料和数值预报资料对发生在副高边缘的两次对流性川西暴雨个例进行对比分析。分析指出:这类暴雨一般发生在中高纬度盛行纬向环流,巴湖-贝湖为宽广槽区,中低纬度维持稳定而强盛的东西向副热带高压环流背景下;高能不稳定及高湿区是这类暴雨易发的温湿能背景条件;当四川盆地以北、以东为高气压区,四川盆地内为低气压区时,有利于此类暴雨的发生。分析又指出:850hPa河套偏东气流的形成与维持以及武都、汉中、安康站和盆地出现3℃左右温差对此类暴雨的发生有提前意义;500hPa北支锋区前沿南压到达青海中部,副高西界东退到盆地西部边缘或北界南落到盆地北部边缘对过程开始具有指示意义。在认识这类暴雨发生背景基础上,合理应用数值预报产品是提高这类暴雨预报准确率的有效途径。 

Thought of Weather Forecast Based on Two Heavy Rainfall Processes in Western Sichuan in Edge of Subtropical High

For heavy rainfall in western Sichuan in edge of subtropical high, as the beginning of no significant impact of the system, storm clouds generated entirely by the basin itself and the development forecasting difficult.The process can be used before the start of the regular observations and numerical forecast data on the edge of subtropical high in the two convective rainfall in Western Case were compared, analysis:This type of storm usually occurs in the prevalence of high-latitude zonal circulation, Lake Toba-Lake Baikal as a broad trough zone, middle and low latitudes as something stable and strong background to the subtropical circulation, surface pressure field is usually presented from north to south, east to the west of the distribution of low state;850hPa easterly flow of the formation of the Loop and Wudu, Hanzhong, Ankang stations and basins to maintain temperature and flow easterly mesoscale heavy rainfall conducive to the occurrence of such;500hPa north branch of the frontal zone south subtropical high pressure, and the west or north south east fall back position to the beginning of the process suitable indicating significance.In understanding the basis of such rainstorms in the background, the detailed analysis of factual information and rational combination of numerical forecast products to improve the forecasting accuracy of such rainstorms effective way.