Used to describe cold weather, this saying derives from the traditional Navy phrase "cold enough to freeze the balls off a brass monkey". This references the brass structure or 'monkey' where cannon balls were stacked.

In the days when gulf wars had more to do with sailing ships than TV coverage, cannon balls were stacked on the decks in pyramids. The pyramids were held in place by a brass frame around the base, called a "monkey". When it got cold, the brass monkey contracted, and the cannon balls rolled off around the ship's deck.

It is often stated that the phrase originated from the use of a brass tray, called a "monkey", to hold cannonballs on warships in the 16th to 18th centuries. Supposedly, in very cold temperatures the "monkey" would contract, causing the balls to fall off.

The phrase 'Brass Monkey Weather' refers to very cold weather that is extremely out of the ordinary; cold enough to freeze the tail, nose and ears of a brass monkey. Example of use: "According to Al Roker next week's weather is going to be so cold, that it'll be real brass monkey weather."