Why Does it Hail in Summer? Plus Photos From Last Night's Storm

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If you were outdoors or looking outside your window last night (Sep 4) between 7 - 9pm, you might have seen a rather spectacular thunderstorm, followed by a brief but dense hailstorm. Hopefully you weren't hit by any of the hailstones!

You might have experienced this hailstorm if you were out last night

Yesterday evening, the Beijing Meteorological Observatory issued yellow hail, yellow thunder and blue wind warnings and announced that there would be scattered thunderstorms in the city until 9pm last night. There were short-term strong winds and hail of magnitude 7 and 8 (10 being catastrophic damage).

Some hailstones from last night's storm

As TBJ editor Katie McCoy reported earlier this year, the capital is no stranger to hailstorms and a few each summer are pretty much guaranteed, but why does hail form in the summer when it's usually hot?

Well firstly let’s take a look at how and why hail actually forms. Hail forms when updrafts (strong currents of rising air) carry water droplets to a high enough altitude to freeze. At this high altitude there are already supercooled water droplets present and these adhere to surface of other water droplets, forming layers of ice around it.

A pile of hailstones from last night's storm

Once a hailstone reaches a large enough weight and size, gravity will begin to act on it and pull it down, however it could be pulled up again by another strong updraft and continue to grow. Therefore when there is an especially strong updraft, large hailstones can form.

The lightning storm last night was brief and spectacular

These strong updrafts occur in cumulonimbus clouds, often called thunderheads or storm clouds which are usually recognisable by their dark, ominous appearance. Although these clouds can occur in winter, they are more commonly seem in summer storms or in tropical areas, hence why Beijing normally experiences hailstorms during summer.

There were reports of extensive damage from Beijing's hailstorm earlier this year

The last hailstorm Beijing experienced in June had some pretty impressively large hailstones, and there were reports of some even being the size of eggs. Videos and photos went viral online showing an array of these large hailstones and the extensive damage some of them had wreaked upon the city.

Many netizens took to comparing the hailstones to eggs

Now, although an egg-sized hailstone may seem to be a rather unusual occurrence, this is nothing compared to a few years ago when there were reports of “coronavirus shaped hailstones” raining down on Beijing. Yes, back in June 2020 during the Dragon Boat Festival there was a particularly violent hailstorm featuring these distinctly shaped stones.

Some of the Coronavirus shaped hail from June 2020

Given that this was still during the pandemic’s relatively early days, many netizens couldn’t help but wonder if this was some kind of apocalyptic sign from the gods. It looks like this time 'round, though, aside from the large size, the hail was relatively normal.

Beijing encounters severe convective weather throughout the year and dense hail falls almost instantly without warning. Citizens are advised to guard against strong convective weather and pay attention to traffic safety when outside.

Images: Annie Han, Victoria Yang, Yamei, Uni You, Weibo

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