a b

c d

Figure 5. Snow crystals approach the form of soft hail, or graupel, as they grow through accretion and freezing of supercooled cloud droplets. Because they are more massive than the droplets, the accreting particles fall more rapidly, colliding with the droplets, which freeze individually. In the first image (a), the original snow-crystal hexagonal shape is still evident. In the second (b), only the basic shape remains. Individual frozen droplets can be seen in all these photographs. As more droplets freeze on the underside of the particle (c), its porous consistency (about two-tenths the density of solid ice) becomes evident. Because the ice accumulates mainly on the downward-facing side, the graupel often grows in a conical shape (d), with the base of the cone down. (With respect to the fall direction of the particles, images a and b are in plan view, and c and d are vertical.)