“It’s brick outside.”
This is New York City slang for cold. My informant has been saying this for as long as he can remember, as well as all of his friends. In fact, most of their speech consists of slang that is informed by creative metaphor and play on words. To more proper English speakers speech in slang might come off as ungroomed, but it often exhibits a high level of sophistication, aesthetic, and active interest in subverting official linguistic norms rather than passively obeying them. It’s highly associated with urban identity, a way to indicate your street smarts. And, in fact, you can count on the brick facade of a New York City brownstone to provide some cooling relief on a hot summer day.