分析2011年2月25—27日张家口市降雪天气过程的高空天气形势，结果表明，降雪期间500 hPa高空在新疆北部是一个深厚的低涡系统，冷低涡不断分裂出小股冷空气东移影响张家口市；850 hPa低涡、暖舌、切变线和低空急流为此次长时间降雪提供了必要条件；26日08：00850 hPa张家口市西部的切变线，是造成降雪的关键性动力系统；25—28日张家口市上空850～700 hPa相对湿度大值区的出现时间与降水时间相吻合，较好的中低层湿度状况为降雪提供了原材料。%The high-altitude situation of a snowfall process happened in Zhangjiakou from February 25 to 27, 2011 was analyzed. The results indicated that 500 hPa height fields over the northern Xinjiang was a deep low vortex system, the cold air continuously broke away from low cold vortex and moved east affecting Zhangjiakou. Low vortex at 850 hPa, warm tongue, shear line and low-level jet provided necessary condi-tions for the snowfall. The shear line at 850 hPa over western Zhangjiakou on February 26 at 08:00 am was the key dynamic system that leading to snowfall. The occurrence time of high value area of relative humidity at 850-700 hPa over Zhangjiakou on February 25 -28 was consistent with the precipitation time, good humidity condition at the mid-low-er layer provided main materials for the snowfall.
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