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."
During the 19th century, it was common to bring these sculptures as souvenirs from China and Japan. The phrase "brass monkey weather" originated from the figurine of the ‘three wise monkeys’ as an image of something sturdy and solid that can only be affected by severe and extreme weather. An early known recorded use of the phrase is in the 1845 New York Sunday Mercury essay 'On Enjoying Life' - "When you love, [...] your heart, hands, feet and flesh are as cold and senseless as the toes of a brass monkey in winter weather".