Are Signs in the Sky Important Prophetic Events?

Why did Messiah state the following about signs in the sky:

"The Pharisees and Sadducees came up, and testing Jesus, they asked Him to show them a sign from heaven. But He replied to them, "When it is evening, you say, 'It will be fair weather, for the sky is red.' "And in the morning, 'There will be a storm today, for the sky is red and threatening.' 

Do you know how to discern the appearance of the sky, but cannot discern the signs of the times? "An evil and adulterous generation seeks after a sign; and a sign will not be given it, except the sign of Jonah." And He left them and went away" (Matthew 16:1-4 NASB).