Normally, frost flowers form during the first hard freeze in late fall. Frost flowers form as water freezes just underground and is forced up through dormant plant tissue. The plant tissue acts as a mold for the ribbons of ice that are then extruded from the ground in the shape of the plant stem.
Several native plants form frost flowers but the species we have here that forms them is White Crownbeard (Verbesina virginica). I suppose the long, sustained cold snap we’ve had this last week allowed them to grow and keep growing until they were covered with snow yesterday. Here are several of the frost flowers I photographed the day before the snow.