2017年2月20—21日宁夏北部暴雪成因分析

Cause Analysis of a Snowstorm Weather Process in Northen Ningxia from February 20 to 21,2017

利用常规气象资料、卫星云图、雷达资料、NCEP再分析资料和EC模式、宁夏WRF等数值预报产品,对2017年2月20—21日出现在宁夏北部暴雪天气的成因进行了系统分析。结果表明:200 hPa西风急流、500 hPa西风槽、700 hPa低层切变线、850 hPa低涡及河套锢囚锋是此次宁夏北部暴雪的主要影响系统;高空西南气流、低空偏南急流、近地面偏东风回流为暴雪输送了充分水汽条件,水汽主要来源于中低层输送;中低层辐合强,高层辐散,“抽吸”作用较为明显,为暴雪提供了较强的动力抬升条件;雷达反射率因子等产品对暴雪的降雪强度、落区预报有较大的实用价值;EC模式、宁夏WRF等数值预报产品对暴雪有较好的预报能力。

The conventional meteorological data,satellite cloud images,radar data,NCEP reanalysis data,and EC,Ningxia WRF and other numerical forecast products are used in this article to make a comprehensive analysis on the cause of the snowstorm in northern Ningxia from February 20 to 21,2017.The results show that the westerly jet in 200 hPa,the west wind trough in 500 hPa,the lower shear line in 700 hPa,the low vortex in 850 hPa and the occluded front in the great bend area of the Yellow Rive are the main factors of this snowstorm.The southwest air current in the upper layer,the southerly jet in low level and the eastward back-flow in near surface,which provides sufficient moisture conditions,and the vapour transport comes from the lowlayer primarily.Convergence in the middle and lower layer with a divergence in the upper layer induces obviouspumping action,which provides sufficient moisture conditions.This analysis proves that radar reflectivity factor and other products have great practical value for snowstorm intensity and fall area forecast and numerical prediction products such as EC and WRF in Ningxia also have a better forecasting capabilities for snowstorm.