There are several guesses as to the origin of that term. Another guess is that the term is taken from El Golfo do las Yequas, the Gulf of the Mares in Spain, referencing the capricious behavior of an Arab mare being much like the winds of the region - mostly gentle, but quite wild when you least expect it. I favor a third guess. That covers brass monkeys, dead horses and more. I wonder what I can dig up for the next article.
Yesterday is history, tomorrow is a mystery, and today is a gift.