I wonder what this means?

When I think of lightning, black skies seem like a foregone thought, but even though there are black clouds in this picture, yet there is quite a bit of clear sky as well. I wonder what it means? People have been looking at the sky since there have been people and Jesus had to deal with those looking for "signs".

Matthew 16:1-4 WEB (R)
(1) The Pharisees and Sadducees came, and testing him, asked him to show them a sign from heaven.
(2) But he answered them, "When it is evening, you say, 'It will be fair weather, for the sky is red.'
(3) In the morning, 'It will be foul weather today, for the sky is red and threatening.' Hypocrites! You know how to discern the appearance of the sky, but you can't discern the signs of the times!
(4) An evil and adulterous generation seeks after a sign, and there will be no sign given to it, except the sign of the prophet Jonah." He left them, and departed.

There is nothing wrong in trying to read the environment; every night there is a weather forecast on TV, the radio and the net. What is wrong is establishing faith in someone based solely on their power to do "miracles". Men have the capacity for trickery and some will use that to deceive the weak minded among us. So, Jesus goes beyond their question and exposes their heart of hypocrisy. He refers to the scriptures about Jonah for signs. Good example to follow; refer to the scriptures, you can't go wrong. Also, it might be a good idea to stay inside during a thunderstorm, even if there is some clear sky out there.