"Red sky at night, shepherds' delight. Red sky in the morning, shepherds take warning"
Shepherds? what about the "sailors"?
the saying has its origins to the time around the 16th century when Spain, France, The Great Britain and Portugal started exploring the high seas to discover new land.
they had formed a system to predict the weather by studying the clouds formations, winds directions and speed.
the system over the past 4-5 centuries has been perfected to the level that even today by observing the wind speed and the change in directions one comes to know how far one is from a storm (if one is about to be formed), if there is goin to be any pressure and temperature change etc etc.
you are entering the vicinity of an area adjecent to the location.