According to the NEA the hail is caused by supercooled water drops that freeze upon contacting particles in the air during thunderstorms. The agency added that pollutants known as PM2.5 and PM10 are only hazardous when inhaled.
According to witnesses heavy rain and dusty winds began at around 3 p.m. in Jurong and Bukit Batok. Later "the wind suddenly turned very cold, and these crystal-like stones started raining down," Laura Tang, 24, who witnessed the event, told Yahoo news.
The last hailstorm reported in Singapore took place on March 27, 2008.