Wood splits much better in cold weather, sub zero makes oak pop open like pinon pine. Steel shivers & shatters more easily then as well, so be sure to wear eye protection using your steel wedge(s) with a hammer, striking steel against steel for any reason in the cold. We used to use the splitting maul or an ax without trouble, but we'd use a wooden club or 'maul' or a big wooden maul called a 'commander' to start the steel wedge into a crack, or use a few home-made wooden wedges (gluts) when possible, more wedges will split out the toughest log in cold weather.
If you ever have to cut down a Dogwood or redbud tree, they make excellent gluts, sharpen a 6" long wedge shape on both ends of a 3' hunk of dogwood, then cut it in half. We'd whittle the bark and a bit of the wood off in a 1.5" ring around the flat end of these gluts and drive on a snug ring of copper, the ring just a ~ 1" chunk sawn off a piece of copper pipe. The wood soon mashes down over the copper, the ring really helps keep it from splitting as you use it. Keep these home made gluts in an unheated shed or barn, they'll last quite a while.