Shelf cloud: What is the strange and terrifying cloud seen in Haridwar?

Arcus clouds are associated with thunderclouds. (Photo Credit Thalia Traianou via Wikimedia Commons)

Rains have battered northern India over the last seven days. Videos of rivers in spate, flooded roads, landslides, and bridges being swept away have been doing the rounds online. One video, which went viral on July 10, is of a spectacular cloud formation over Haridwar in Uttarakhand. In it, you can see massive grey clouds that resemble a towering wall. The meteorological occurrence, known as an Arcus cloud, drew a lot of attention on social media. Many were curious to know the reason behind its formation.

So, what is an Arcus cloud? And why was it seen in Haridwar? Let’s find out.

What are Arcus clouds?

These are low-level, long and thin cloud formations that are often associated with powerful storm systems such as thunderstorms. At times, they can be seen below cumulonimbus clouds (more commonly known as thunderclouds). Every once in a while, they also occur with cumulus clouds.

Arcus clouds come in a range of shapes and sizes, and can be quite spectacular to see. They usually form when cold air from a thunderstorm pushes warm, moist air upwards. As the warm air rises, it cools and condenses into clouds. Wind direction influences the new cloud formation.

You could get a “shelf cloud”, such as the one seen in Haridwar, which is attached to the existing storm cloud. Or, a “roll cloud”, which is basically a horizontal column that is separated from it. Either way, an Arcus cloud lasts for a short period of time.

Are they dangerous?

Since these clouds usually form with thunderclouds and downdrafts, they are associated with strong wind gusts, heavy rain or hail. Thunder and lightning are common too. In extreme cases, a tornado can occur and destroy everything in its path.

Yet, they aren’t a threat to human life. More often than not, an Arcus cloud acts as a warning of an approaching powerful thunderstorm or an extreme weather event. They do not occur if a storm is relatively weak, and are often seen at the location where the strongest lightning and thunder can occur. So, knowing how to identify them can give you time to seek cover and save lives.

Is it rare?

While it may have looked grey, menacing and unusual in the viral video from Haridwar, Arcus clouds are actually not-uncommon in India. A quick Google search will show that the clouds have been seen in Kolkata, Madurai, Mumbai, Chennai, and several other Indian cities in the monsoon months. They are also seen around the world routinely in places such as Australia, Alaska, California, etc., during powerful thunderstorms.

So, the next time you see an Arcus cloud in the sky, take a minute or two to appreciate its beauty. Then, head for cover.