As I write this I am looking out my window and there is not a cloud in the sky, birds are singing, people are out and its warm. Last Tuesday it was not warm. In the early afternoon we experienced a freak hail storm, followed by thunder and lightning. The photo above is from Thorndon Quay (one of the areas that was heaviest hit). The storm caused some homes to lose power and 2 car crashes were attributed to be directly caused by the weather.
Hail is formed in areas that experience high updraft such as in severe weather systems. The updraft will cause the air to rise, as it does it gets supercooled and falls back within the cloud. If the updraft is strong enough this process will repeat until the updraft can not support the weight of the hailstone. At this point the hail stone will fall to earth. Because of the way they are formed hailstones are constructed of thin layers of ice, much like an onion.
This photo along with another one I took was also uploaded to Weird Wellington. A website documenting the strange occurrences that happen in this small city. To check out the second photo (along with some others) click here.