Weather in Baicheng, Jilin

A, 65438+10.4, cloudy day and night, covered by clouds, less solar radiation will reach the ground, and the temperature will not be too high. At night, the inverse radiation of clouds will be stronger, and the heat lost from the ground will be less, so the temperature will not be too low. The average temperature will not be the highest, so it does not meet the problem.

B, 65438+10.5, sunny, with more solar radiation reaching the ground and higher temperature. On a clear night, ground radiation and low temperature lose more heat. The temperature difference between day and night is the largest, so it is correct;

C, 65438+10.6, sunny day, high temperature, less heat loss on cloudy days at night, high average temperature, frost is not easy to appear, which does not meet the meaning of the question;

D, 65438+10.5, sunny, with more solar radiation reaching the ground and higher temperature; On a clear night, the ground radiation loses a lot of heat and the temperature is low. The temperature difference between day and night is the largest, so it is impossible for a cold front to pass by, which does not meet the meaning of the question.

Therefore, choose: B.