We don’t often get hail here in Vacaville, so it might be good to remind ourselves how hail is formed. Hail starts out as a raindrop. The raindrop was heavy enough to start falling, when it got pushed up by an updraft in the thunderstorm. If you’ve climbed a mountain, you might notice that it tends to be colder the higher we travel up. Those raindrops get pushed so high up, they get above the freezing point and begin to freeze. They might get heavier, start to sink and then get pushed up again when they get in an updraft. This up and down motion causes layers to form, which gives hailstones rings. Eventually, the hail will get too heavy to get pushed back up, and then falls to the ground. If the stones are large enough, they stay as hail all the way to the ground, even though the lower levels of atmosphere are warmer.
The weather needed to make hail is similar to tornado weather. They both require low level moisture, lift, wind shear, and atmospheric instability. Hail and tornadoes both occur during thunderstorms. Other forms of precipitation don’t always require a thunderstorm. Sleet happens in the winter when snowflakes melt then refreeze. Freezing rain stays as rain all the way to the ground, which is cold enough to freeze the rain into a slippery ice sheet on the ground. While hail and sleet might cause damage by hitting things and breaking them, the icy coat of freezing rain can coat a surface, bringing down branches and power lines with the added weight.
Hailstones can get pretty big. While most meteorologists would measure hailstones in inches or centimeters, it is popular to compare hailstones to coins or balls, like soft balls. Don’t compare them to marbles, because marbles come in too many different sizes. Hailstones larger than 1 inch, or a quarter, are considered severe while a 2 inch diameter is considered significant. The largest hailstone on record fell in South Dakota. It was 8 inches in diameter and weighed 2 pounds.