The following are the main characteristics of the general circulation of atmosphere in May 2013. There is one polar vortex center in the Northern Hemisphere, and the strength is 2-4 dagpm lower than normal years. The circulation presents a four wave pattern in high latitudes, of which there is a cut off low votex in Novosibirsk, bringing cold air mass to Northern Xinjiang. The south branch trough is more active than normal years. Monsoon starts earlier than normal years over South China Sea, and the subtropical high moves towards west and north gradually. The monthly mean temperature is 16.9℃, which is 0.7℃ warmer than normal years. The national average precipitation is 85.5 mm, which is 23% more than the normal and recorded as the 2nd largest amount for the corresponding period since 1961. The main weather characteristics in this month is as follows: heavy rainfalls occur in Southern China frequently, high winds and hails hit more than 20 provinces and cities, and one sand dust event is seen in the Northern China.