Hailstones causes billions in damage in the U.S. alone, but meteorologists know little about how they form. A new study using isotope analysis successfully recreated the “history” of 27 hailstones as they formed in nine separate storms across China. This data shows that hailstones primarily form by descending steadily or pushing upward in an updraft only once, which is in contrast to the traditional idea that hailstones form in a recycling process inside a storm cloud. Related Story This Dark Ocean Pit Has a Bleak Weather Forecast“This work fundamentally changes how we understand hail formation,” Zhang said in a press statement. However, Zhang’s data showed that embryos of hailstones can actually form outside that gradient, between about -33.4 and -8.7 degrees Celsius.