‘And he said to the crowds also, “When you see a cloud rising in the west, straight away you say, ‘There comes a shower,' and so it happens.”
Jesus has now turned His concentration back on the crowds who have been drinking in His words, even if they have failed to fully understand them. He draws their attention to weather signs which they use in order to know what weather to expect. A cloud rising in the west will be coming in from the sea and will therefore contain a large quantity of water which is just waiting to fall once it is affected by land. Thus such a cloud regularly indicates rain.