Typically we think of frost cracks or sunscald when the crack is on the south or south-west side. Whether that's the case here I wouldn't know and I'm a generalist not an arborist. I read an interesting article a while back that suggests frost cracks and sunscald may not be quite what they seem to be (the PDF jumps a bit between pages so one has to scroll past an intervening article to read the whole thing:
