Parts of the United Arab Emirates appeared to be blanketed in snow today after a hailstorm passed through some of the country, including the city of Dubai — located in the middle of a tropical desert.

Observers on social media posted gleeful shots of handfuls of gathered ice pellets and sheets of hail pummeling cars and streets. But how do frozen ice chunks form in a place much better known for sandstorms than hailstorms?

Hail tends to form best when the air is warm, moist, and stormy. The process is specifically tied to very strong updrafts that carry wet air high into the atmosphere. And, of course, the higher the moist air goes, the colder it gets. The air temperature outside an airplane flying at 30,000 feet is typically around negative-50 degrees Fahrenheit, and even over the desert it’s cold enough to freeze moisture in the air in a heartbeat.

Even a moderate thunderstorm can reach heights of 40,000 feet. Of course, ice is heavy — once it forms inside the storm it will want to fall to the earth. But if the updraft is strong enough, it will convect back up again. With each convection, another layer of ice forms around the hail stone. This process repeats until the weight of the stone is too much for the updraft to hold and it falls to the ground. The size of the hailstones is, therefore, mostly dependent not on temperature but on the strength of the thunderstorm.

Anywhere in the world that has thunderstorms can have hailstorms, and they occur most frequently in areas that are warm and wet. In the United States, the region where Nebraska, Colorado, and Wyoming meet is known as “Hail Alley,” and it sees about eight hail events per year on average. Parts of India, southern China, Australia, and Kenya are also particularly prone to hailstorms.

In other words, hailstorms have little to do with the climate on the ground, and are caused instead by the meteorological processes high up in the air. Even a place like Dubai can be thumped by hail from time to time.

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