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Waves in the sky amaze as clouds put on a show in unusual conditions

Published: 01 May. 2025, 19:55 Updated: 01 May. 2025, 22:16

Asperitas clouds spotted on May 1. [JOONGANG ILBO]

Wave-shaped clouds resembling rough sea waves were spotted over Seoul on Thursday, caused by atmospheric instability as cold and warm air masses collided.

A rain cloud system flowing in from the Yellow Sea moved eastward throughout the day, bringing rainfall to many parts of the country, including the capital region, according to the Korea Meteorological Administration (KMA). Some areas also reported thunder, lightning and soft hail due to unstable atmospheric conditions.

Photos and posts describing the rare cloud formation appeared on social media platforms such as X.

“It looks like rough waves are crashing in the sky,” wrote one user. “I've never seen clouds like this before.” Another said, “It feels like something extraordinary is about to happen,” expressing awe at the sight.

The cloud formation is officially known as asperitas, a name derived from Latin meaning “rough” or “uneven.”

Asperitas clouds spotted on May 1. [JOONGANG ILBO]

When air pockets within the clouds become unstable, wave-like motions are generated and trapped inside the cloud mass. These vertical movements cause the underside of the cloud to ripple dramatically, creating a visual effect reminiscent of a choppy sea surface.

The World Meteorological Organization added asperitas clouds to the "International Cloud Atlas" in 2017, formally recognizing the phenomenon.

“This type of cloud forms when strong cold air flows in the upper atmosphere while warm air rises from below, creating significant atmospheric instability,” said Woo Jin-kyu, a forecaster at the KMA.

Asperitas clouds spotted on May 1. [JOONGANG ILBO]

Heavy rain and unstable weather are expected to continue across the country through Thursday night. As of 1 p.m., a strong wind advisory was in effect along the west coast, and a heavy rain advisory had been issued for mountainous areas of Jeju Island.

“There will be localized downpours of 10 to 20 millimeters (0.39 to 0.79 inches) per hour accompanied by gusty winds, thunder and lightning,” the KMA said Thursday. “Some regions may also experience soft hail, so we urge the public to take precautions to protect crops, facilities and personal safety.”

The upcoming long weekend will also see intermittent rain. Skies will remain mostly clear nationwide on Friday. However, light rain is forecast for Saturday, particularly in the afternoon, with southern regions seeing precipitation into the evening.

Asperitas clouds spotted on May 1. [JOONGANG ILBO]

On Children’s Day, which falls on Monday, rain is expected in Jeju in the afternoon. Showers are also predicted for central regions and North Jeolla on Monday afternoon.

With on-and-off rain expected, temperatures are likely to fall slightly, staying near or below seasonal averages. A large temperature gap between day and night is also expected, prompting health officials to advise caution for those spending time outdoors.

Translated from the JoongAng Ilbo using generative AI and edited by Korea JoongAng Daily staff.
BY CHON KWON-PIL [[email protected]]