How does hail form?
It was a wild Wednesday afternoon in the Twin Cities as severe weather passed through the area. Large hail fell near Plymouth and Maple Grove up to two inches in diameter. “That’s ping pong to tennis ball size hail,” said WCCO-TV meteorologist Paul Douglas. But how does hail actually form? The first thing you need are the cumulonimbi clouds that make the anvil heads,” said WCCO-TV meteorologist Chris Shaffer. “Those are the ones creating the strongest updrafts that kick air up into the atmosphere.” Hail begins as water droplets that are then pushed up into freezing cold air by those updrafts. “They keep kicking that piece of hail higher and higher in the atmosphere,” said Shaffer. That’s where it collides with more water and refreezes. “It just grows and grows,” said Shaffer. “They grow by a process called excretion. Eventually they become too heavy and just fall from the sky. The stronger the storm is, the better the chance for hail to grow.” Hail that reaches the ground is generally
Hail forms when tiny clumps of ice, kept aloft by strong updraughts, get blown through freezing thunderclouds until they are heavy enough to fall to earth. Most large thunderstorms create some hail, but conditions must be met if the hailstones are to grow large, freeze solid, and survive until they reach the ground. Ideal conditions for hail are tall clouds that reach high into the atmosphere, many swirling updrafts such as in a tornado, and cold temperatures within and beneath the storm. Every hailstone begins to form as an ice nucleus, a small cluster of supercooled water droplets or clumps of snow. This center is called a graupel, and it may continue to accumulate ice, melt in the thundercloud and turn to rain, or be smashed apart by other graupels. If a bug, piece of bark, seed, or stick gets blown up into the storm cloud, it creates another possible nucleus for a hailstone. If the thunderstorm is cold and windy enough, this graupel will accumulate layers of ice the way a dipped ca
There are two ideas about hail formation. In the past, the prevailing thought was that hailstones grow by colliding with supercooled water drops. Supercooled water will freeze on contact with ice crystals, frozen rain drops, dust or some other nuclei. Thunderstorms that have a strong updraft keep lifting the hailstones up to the top of the cloud where they encounter more supercooled water and continue to grow. The hail falls when the thunderstorm’s updraft can no longer support the weight of the ice or the updraft weakens. The stronger the updraft the larger the hailstone can grow. Recent studies suggest that supercooled water may accumulate on frozen particles near the back-side of the storm as they are pushed forward across and above the updraft by the prevailing winds near the top of the storm. Eventually, the hailstones encounter downdraft air and fall to the ground. Hailstones grow two ways: by wet growth or dry growth processes. In wet growth, a tiny piece of ice is in an area wh
It starts out as falling rain, several miles up in the clouds. But an updraft(an upward blowing wind) holds it aloft, moving it upward instead of allowing it to fall. As it goes up, it freezes because of the colder temperatures aloft. Drops of supercooled water(agitated liquid water colder than 32 degrees) hit these pellets of ice and freeze on. The mass of ice may fall and then be lifted again several times, each time getting larger and larger as more water freezes onto it. When the hail is so big that the updraft can’t hold it aloft any more, it falls to the ground. Other times, the updraft may weaken, or shift its position and the hail falls because of that. The stronger the updraft is, the larger the hail can be. It takes an updraft of 55+ mph to create hail the size of a golf ball, and an updraft of 90+ or more mph to create hail the size of a baseball. It usually takes hail the size of a hen’s egg to dent a car, but hail the size of baseballs can kill animals who can’t find a she
