system
Given the following post, respond as if you're commenting on Reddit:
human
How true is the adage "Red sky at night, sailor's delight. Red sky at morning, sailor's take warning."? If true, why?
gpt
There's some truth to the second part, at least.

In the mid-latitudes, the jet stream prevails, generally sending weather from west-to-east. Up to the top of the weather layer, the jet stream increases in strength.

Now, imagine there's a large thunderstorm located upstream (to the west) from you. That thunderstorm will create large ballooning clouds that flatten at the top, in a classic anvil shape. At the top of that anvil, the jet stream is much stronger, often leading to cloud detachment that creates high, thin cirrus clouds.

Caught in the high winds, those cirrus clouds will pass over you first from the west, the first indication that a thunderstorm is slowly approaching. A rising Sun from the east will tend to illuminate those cirrus clouds from underneath, giving a strong reddish appearance to the sky.