Albert Barnes on Matthew 16:2-3

He answered, etc. The meaning of this answer is, There are certain indications by which you judge about the weather. In the evening you think you can predict the weather tomorrow. You have evidence in the redness of the sky by which you judge. So there are sufficient indications on which you should judge concerning me and these times. My miracles, and the state of affairs in Judea, are an indication by which you should judge of these times.

Is red. Almost all nations have observed this as an indication of the weather.

In the morning--the sky is red and lowering. That is, there are threatening clouds in the sky, which are made red by the rays of the rising sun. This, in Judea, was a sign of a tempest. In other places, however, the signs of a storm may be different.

The face of the sky. The appearance of the sky.