中低层切变线引起的持续性降雪天气分析

Analysis of Continuous Snowfall Caused by Shear Line in Middle and Low Layer

摘要: 本文利用NCEP再分析数据对一次降雪过程进行诊断分析，得出高层主要影响系统为低涡，中低层影响系统为切变线；此外，中低层切变线的存在和维持是降雪持续时间较长的主要原因，切变线维持的主要原因是中层冷空气的补充渗透；此次天气过程伴随南支槽和副热带高压的活动，南支槽前部的西南气流和副热带高压西侧的西南气流为降水形成输送了大量暖湿空气，是降水形成的主要水汽来源；中低层比湿对降雪强度的预报有很好的指示作用，而低层相对湿度大值区的分布对降雪起止时间的预报有很好指示意义；建议预报员服务保障过程中采取持续跟进、递进补给的服务方式，在发布各类预报预警信息时可以根据提前量逐步细化预报结论，做到先提醒、再预警。

Abstract: In this paper, NCEP reanalysis data is used to diagnose a snowfall process, and it is concluded that the main influence system of high level is vortex, and the influence system of middle and low level is shear line; in addition, the existence and maintenance of shear line of middle and low level are the main reason for the long duration of snowfall, and the main reason for the maintenance of shear line is the supplementary infiltration of cold air in the middle level; this weather process is accompanied by the South Branch trough with the activity of subtropical high, the southwest air flow in the front of the South Branch trough and the southwest air flow in the west of the subtropical high transport a lot of warm and wet air for precipitation formation, which is the main water vapor source of precipitation formation; the specific humidity in the middle and lower layers has a good indication for the prediction of snowfall intensity, and the distribution of the high value area of relative humidity in the lower layers has a good indication for the prediction of the starting and ending time of snowfall; suggestions in the process of service support, the forecaster adopts the service mode of continuous follow-up and progressive supply. When releasing all kinds of forecast and early warning information, the forecaster can gradually refine the forecast conclusion according to the advance amount, so as to remind first and then early warning.