Haze, rain and now hail?

As small pieces of ice rained down on Tuesday afternoon, Singaporeans were shocked to find the frozen bits falling instead of rainwater. An uncommon sight in Singapore, the hailstorm took many on the typically sunny island by surprise.

What is hail?

A frozen precipitation, hailstones are the pieces of supercooled droplets that fall in a thunderstorm, or a hailstorm. Hail occurs mostly in storms when the temperature falls below freezing point and strong winds keep the droplets up in the cool region, causing them to turn into ice.

This wind, known as the updraft, prevents liquid rain droplets from falling to the ground and instead persistently pushes it higher, where the temperatures are lower. When more rainwater and dirt particles form around the hailstone, it gradually grows larger until it becomes too heavy to be blown up by the updraft. At this point, it falls to the earth as a hailstone.

Generally, hailstones become larger if the updraft wind is stronger, as more water and particles can form around the ice.

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Why was there hail in Singapore?

While the National Environment Agency (NEA) in Singapore has confirmed that the hail three days ago was not caused by cloud seeding done by our neighbouring countries, the authorities could not confirm whether the haze had any part in causing the hail.

Hail, usually caused by intense thunderstorms and the cooling of large water droplets, is quite rare in Singapore. Tuesday’s brow-raising phenomenon saw suitable conditions for hailstones to form, resulting in the hail in Singapore.

An eyewitness, Ms Joycelyn Chen, experienced the hail in the Choa Chu Kang area locally. She recounts that it was “raining ice”, and that she could “hear the sound of the ice hitting the ground.”

Which parts of Singapore were hit by the hail?

The island’s western residents experienced most of the hail action early this week, with those living in areas like Jurong and Bukit Batok having first-hand encounters with the hail in Singapore. Those who saw the bits of ice fall immediately snapped shots and videos of it, intrigued by the unusual sight.

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Is hail very common?

While uncommon in Singapore, hail in the rest of the world is a less rare phenomenon, with places in the temperate regions seeing it more frequently. In Singapore, however, hail was last reported five years ago in 2008.

The unexpected weather conditions as well as the heavy thunderstorms that triggered the hail in Singapore have cause inconveniences in the form of fallen trees and obstructions in its aftermath. While the shower somewhat cleared the air of the previously persistent haze, the authorities are still advising Singaporeans to not take the situation too lightly yet.

With the dropping Pollution Standard Index (PSI) in the wake of the rain, some Singaporeans might believe it is already safe to resume outdoor activities. However, it is still encouraged that families exercise caution with regard to the haze as although the PSI has fallen, the PM 2.5 reading is still in the unhealthy range despite the showers.

Watch the video below for a first-hand encounter with the hail in Singapore: