The Italians would say: "fa un freddo cane." It's dog-cold. As a dog lover, I personally take exception to dragging those charming beings into derogatory expressions, as when we English-speakers compare an objectionable woman to a female canine. The French say: "il fait un froid de canard." It's duck-cold. How do the Europeans think they're going to unite when they can't even agree on important matters like this? And the latter expression reminded me of J.D. Salinger's departure yesterday, when many commenters (including Italians) remembered Holden's musing about where the ducks go when the pond freezes over. Where do they go? Where do the canards go when il fait un froid de canard?
Getting back to the Italian. If you want to be even more refined, you can say "fa un freddo boia." It's hangman-cold.
Good news. I just checked the weather thingy and it's gone up to six degrees.