Red Sky in the Morning
Red sky in the morning, sailors take warning. Red sky at night, sailors delight.
That's how I remember it. Wikipedia remembers it a little differently, with several variants.
I like this one.
“Like a red morn that ever yet betokened,William Shakespeare
Wreck to the seaman, tempest to the field,
Sorrow to the shepherds, woe unto the birds,
Gusts and foul flaws to herdmen and to herds.”