Winter ends long before there are no more frosts. *I'll guess our last significant frost tends to be in late April, but winter is over in March. *Not because of the vernal equinox, but because the beginning of March is more like winter and the end of March is more like Spring. *It can still snow after that, but the life expectancy of a late snow is pretty short after the sun comes out. *But there's no doubt winter hangs on in NE Montana long after it's gone from central CT.