The phenomenon of the castle can be seen in the warmer months. Hail is formed in cumulonimbus clouds. These clouds are very powerful, they can reach sizes of about 12-14 miles.
Warm currents of air rise up, pick up a hailstone, formed in cumulonimbus cloud. Picked up hailstones begin again to fall and once in the lower cold layers of clouds, covered with ice. Here the ascending warm air stream again entice hailstones up, after which they again begin to fall... This continues up until the hailstone is not made of such size and weight, which will not be able to stay in the air and fall to the ground.
Dimensions than hailstones are very different, sometimes they are a chicken egg. There are cases (though these are very few), when the weight of one hailstone reached one kilogram!