Hail

What's that tap tap tapping on the roof? It's hail. Thank goodness the car's in the garage. The storm didn't last very long, and the ice balls were only the size of peas.

Hail is formed through a sort-of roller coaster ride through intense thunderstorms. Strong air currents lift small ice pellets high into the middle and upper portions of a cumulonimbus cloud. This is where super-cooled water droplets collide and the ice pellet grows through a process called accretion. Once the pellet is too heavy for the updrafts to keep it airborne, it begins to fall, and if it does not melt completely before reaching ground level, it comes out as hail. A little internet research enlightened me that hail can be classified into three stages of development, Grauple, Small Hail, and Hailstones.

Grauple are soft snowflake-like stuctures that bounce off hard surfaces. We usually call it snow pellets.
Small hail: Has a higher density than grauple, and are usually semitransparent and rounded, with diameters up to 1/5 inch. They consist partly of liquid water and sometimes have a frozen outer shell. Graupel transforms into small hail by the liquid water taken in through air capillaries in the ice framework.
Hailstones: Round stones of ice, with layers that look like an onion. Layers are formed during the stones and rise and fall within the storm cloud. During the a decent, the outer layer of ice melts slightly, and then re-freezes when updrafts carry the hail back up into freezing temperatures. The more clear the hailstone is, the slower the freezing process. The more opaque (milky) the hailstone is, the faster the freezing process.

Our little pea-sized pellets are pikers compared to the Largest Hailstone Ever Reported:
September 3rd, 1970 Coffeyville, KS 1.67 lbs, 17.5 in in circumference, 5.5in in diameter
(about the size of a softball.)