The weather in Nanchang on May 3rd.

According to the meaning of the question, the weather system shown here is a cold front crossing.

A, the warm air mass is strong, which pushes the front surface to move to one side of the cold air mass, forming a warm front, so it does not meet the meaning of the question;

B, the cold air mass is strong, and the front formed by pushing the front to move to the side of the warm air mass is a cold front, which does not meet the meaning of the question;

C, the picture shows that there is an anticyclone in the southern hemisphere, so it does not meet the meaning of the question;

D. The picture shows a cyclone in the northern hemisphere, so it doesn't fit the question.

So the answer is: B.