You know how to read the sky, but do you know how to read the times? Jesus points out a common human ability that highlights a spiritual failure.
Jesus addresses the crowds with a striking observation about their everyday wisdom. They can look up at the sky, see a cloud rising from the west (over the Mediterranean Sea), and immediately know that rain is coming. This is practical, immediate knowledge, and it's always accurate. They don't doubt it; they accept it as fact. This ability to discern and predict based on clear signs is something they do without hesitation.
But Jesus uses this as a setup. He's gently calling out their spiritual blindness. They are experts at reading the weather, but they are missing the most important 'signs of the times' right in front of them – His own presence and ministry. Their ability to predict rain shows they can discern, but they choose not to apply that discernment to the divine.