利用1961—2019年降雪期乌鲁木齐市5个国家气象站日降水资料、NCEP逐日4次0.25°×0.25°和1°×1°再分析资料,统计分析乌鲁木齐市暴雪特征及大尺度环流形势,归纳出现暴雪的3种典型环流类型,并分别选取典型个例进行诊断和对比分析。结果表明：（1） 乌鲁木齐市暴雪发生频率以0.3次·(10a)^-1趋势上升,具有准20 a振荡周期,发生次数最多为3月（40%）,11月次之（32%）。（2） 乌鲁木齐市暴雪分为槽前西南气流型、高空槽东移型和强锋区型,强锋区型比例最高但降雪量小,槽前西南气流型持续时间长且降雪量最大,高空槽东移型最少但影响面积更大且雪强更强。（3） 乌鲁木齐市暴雪的主要影响系统为300 hPa极锋急流、500 hPa偏西或西南气流、700 hPa低空偏北急流和850 hPa西北气流。（4） 形成乌鲁木齐市暴雪的机制为低层偏北气流遇山堆积迫使暖湿空气抬升形成“冷垫”,并与500 hPa以上西南气流形成强垂直风切变和深厚的锋生区,但因三类过程强锋生维持时间和锋面斜率与伸展高度的不同使产生暴雪的原因有明显差异。（5） 暴雪的水汽输送主要为西南、偏西和西北路径,槽前西南气流型和高空槽东移型在西南气流引导下直接输送至暴雪区上空,强锋区型则由水汽的接力输送形成水汽汇合。本研究对乌鲁木齐市暴雪天气系统结构特征进行了分类和归纳,为预报服务提供有效参考依据。

The area along the northern slope of the Tianshan Mountains has a high incidence of snowstorms in northern Xinjiang, China. As one of the main cities, Urumqi City has essential research value. Our research is based on the daily precipitation data of five national weather stations in Urumqi City during the snowfall period from 1961 to 2019 (November to March of the following year) and NCEP reanalysis data of 0.25°×0.25° and 1°×1° 4 times a day. Fifty-three times the characteristics of the snowstorm process and the large-scale circulation background are analyzed and summarized. Additionally, the Urumqi City snowstorm impact system is classified. Furthermore, the high and low altitude configurations of different types of snowstorms are synthesized and analyzed to obtain the structural characteristics of various systems. The results are as follows. (1) The frequency of snowstorms in Urumqi City increased by 0.3 times·(10a)^-1, with a quasi-20-year oscillation period and the highest frequency of occurrence in March (40%), followed by November (32%). (2) The snowstorm in Urumqi City is divided into southwest airflow in front of the trough, eastward movement of the upper-altitude trough, and strong front area. The strong front area has the highest proportion, but the snowfall is small. The southwest airflow in front of the trough lasts for a long time, and the snowfall is the largest. The east-moving type is the least. Meanwhile, the affected area is larger, and the snow intensity is stronger. (3) The main impact systems of the snowstorm in Urumqi City are 300 hPa polar front jet, 500 hPa west or southwest airflow, 700 hPa low altitude northerly jet, and 850 hPa northwest. (4) The mechanism of the formation of the Urumqi City snowstorm is that the low-level northerly airflow meets the mountain accumulation to force the warm and humid air to uplift to form a “cold cushion”, and form a strong vertical wind shear and a deep frontogenesis zone with the southwest airflow above 500 hPa. However, the causes of the snowstorm are different due to the difference in the duration of the strong frontogenesis and front slope and extension height of the three processes. (5) The water vapor transport of the snowstorm is mainly southwest, west and northwest, and the southwest airflow pattern and high altitude in front of the trough. The eastward trough type is guided by the southwest airflow and is directly transported to the sky over the snowstorm area. In contrast, the strong front type is transported by the relay of water vapor to form a water vapor confluence. We summarized the system structure characteristics of Urumqi City snowstorm weather caused by different influence systems. Consequently, we obtained that there are significant differences. Further research can improve the understanding of the evolution process of snowstorms along the Tianshan Mountains in northern Xinjiang. By combing forecast ideas, we can provide effective forecast services reference basis.