The "Red sky at night..." expression, more commonly delivered in a
nautical vein - "...
sailor's delight; red sky at morning, sailors take warning" is actually based somewhat in
fact, at least in the
tropical latitudes where
Trade Winds blow (and sailors used to
ply their
trade).
The "red sky" typically appears when the
sun is low on the
horizon shining light up onto the underside of a broad
cloud deck, as one finds in
storm systems. Since the Trade Winds blow roughly from
east to
west and the sun
rises in the east, a red sky at morning means there is likely a storm
upwind of one's location, and it will arrive before too long.
Conversely, a red sky to the west, where the sun is
setting indicates that either a storm system has passed or one that has developed will be moving away.
Pretty much the
reverse applies in the
mid-latitudes, about 30-50
degrees north or south (
United States,
Southern Europe,
China,
Argentina), where the wind blows from the west (
westerlies).