Based on the data ofbasic observation and numerical forecasting productT639, the causes ofa sandstorm weatherprocess occurred on April13, 2009 in the south of JunggarBasin were analyzed. The results show itwas caused by the north-west strong cold air. The continual temperature rising provided the favorable thermal condition for sandstorm, and theWestSiberian cold troughmoving towards southeastand developing greatly provided the dynamical condition for it. The vertical structure ofSiberian cold trough provided themechanism ofmomentum transmitting downwards for sandstorm. The upper and lower level jet stream made the frontal zone at the middle and lower troposphere strengthen and atmospheric stratification unstable, which provided a favorable large-scale circulation environment. The development and persistence ofdry-warmer tonguewas an omen for its occurrence. The strong sandstorm occurred in the rear of the cold front, the frontof the cold high pressure and the airflow divergence zone. Moreover, the special terrain also provided a favorable geographical condition.
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