In winter, the strong cold surge moves to the sea from land. Because the temperature over the sea water is relatively warmer, weak convection start to generate near the sea and cumulus clouds start to develop. However, these cumulus clouds are suppressed by the sinking motion of the cold air, the cumulus clouds will only grow to a certain height. Hence no new cloud will be produced beside the original Cu. In this way, cumulus clouds arranged in parallel line will be produced on the sea, which is the so-called cloud street. The stronger the cold air, the longer and smoother the cloud street can extend.