Nevertheless, all snowflakes are built according to the same principle. Each snowflake has a hexagonal core from which icy rays grow. They branch like small branches, forming stars or hexagonal rods. Different growth rates in different directions lead to the fact that there are always new forms. The growth rate depends, among other things, on the temperature. The flakes change constantly. When they fall, they grow, get caught or melt again. Fine-grained powder snow is produced in very cold, low-water vapour air. If it is warmer, large flakes fall. Alternating freezing and thawing turns a snowflake into a grain of sleet or hail. Typical six-jet snow stars are formed when temperatures in the clouds range from 12 to 22 degrees Celsius below freezing. Why do we often wait in vain for snow around Christmas? The weather is divided into three parts in December: The beginning is usually unusually mild, the second third grimly cold and the last mild and rainy again. This is because in the last third there is often a western weather situation that brings mild and humid air from the Atlantic. And that’s why the snow often thaws away shortly before Christmas.