John Gill Commentary Luke 12:54

"And he said to the multitudes also, When ye see a cloud rising in the west, straightway ye say, There cometh a shower; and so it cometh to pass." — Luke 12:54 (ASV)

And he said also to the people
For what Christ had before said, were chiefly, if not solely, directed to his disciples; but now he turned himself to the innumerable multitude that were about him, and particularly addressed himself to the Scribes and Pharisees that were among them:

when you see a cloud rise out of the west ;
the watery vapours being attracted by the heat of the sun, out of the Mediterranean Sea, which lies west of the land of Judea, and formed into a cloud, and drove by the wind:

immediately you say a shower is coming ;
as soon as it is seen, it is immediately concluded and affirmed, that a very heavy shower will soon fall, it having been frequently observed so to do, when this has been the case:

and so it is ;
for the most part, there commonly follows a large shower on such an appearance, and they were seldom mistaken in their conclusions.