Based on the observation data of MICAPS, this paper analyzed the strong temperature drop in the Inner Mongolia Reach during 20-23 November, 2016. The results show that the strong temperature drop leading to the rapid freeze-up of the river is closely related to the vertical trough in the vicinity of the Beihu Lake. There is a high pressure ridge development over 500hPa from the Caspian Sea to the West Siberian Plain, of which the ridge collapse is the forecast key of the vertical and strong cold air to the south. With the high-altitude transverse trough to the vertical south, the small high-pressure split out of the ground cold high-pressure constantly moving southward and influence the Inner Mongolia River. The cold troughs in the lower reaches of Inner Mongolia have been intensified during the course of the movement, and the strong cold advection occurred under the northerly winds, which aggravated the temperature gradients in the Inner Mongolia Reach and resulted in the strong cold air weather. When a large number of cold air accumulated in the northern lowlands of Siberia, and a typical weather situation activated, forecasters should consider that the Inner Mongolia will have strong cooling process. At the same time, if the river flow is small, with each station along the river dropped by a cold wave standard in 48h, and the biggest drop is beyond 14℃, forecasters should consider that the Inner Mongolia will quickly change from the ice flow to freeze up.%利用常规观测资料,对2016年11月20～23日内蒙河段强降温天气过程进行诊断分析.结果 表明:造成这次快速封河的强降温天气过程,与贝湖附近的横槽转竖密切相关.500hPa上由里海到西西伯利亚平原上空有高压脊强烈发展,脊崩溃是横槽转竖及强冷空气向南爆发的预报着眼点.随着高空横槽转竖并南下,从地面冷高压主体分裂出来的小高压不断东移南下影响内蒙河段.低层冷槽在移动过程中不断加强,并在偏北风急流作用下产生强冷平流,加剧了内蒙河段的温度梯度,共同造成了本次内蒙河段强冷空气天气过程.当北西伯利亚低地出现大量冷空气堆积,且有典型天气形势配合冷空气活动时,要考虑内蒙地区将有强降温过程;如遇内蒙河段河道流量较小,在沿河各站48h降幅达到寒潮标准,最大降幅在14℃以上时,要考虑内蒙河段从流凌到封河的历时将会较短.
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