Quickly to mind are the similes I often hear in the Midwest
-Cold enough to freeze the balls off a brass monkey
-cold as a witch's title
-cold as a well diggers belt buckle in Alaska
An internet search revealed this one which makes me shiver
-"cold as a loveless duty done" - M. L. Anderson
And a goody from Shakespeare "cold as a dead man's nose"
All this talk of just how cold it can get reminds of a winter in the 80's when we had temps of 14° below 0 with wind chills of 20 below. We still had a good sized dairy goat herd that required milking twice a day. With each step I took my boots stuck to the icy ground as with each breath my nostrils froze together for the briefest of moments. So cold until I reached my seat between two warm does.