Yesterday my social media was inundated with pictures of a fallstreak cloud, or hole punch cloud, seen over western parts of the Avalon Peninsula. Along with that, I was asked the question, how do these form? Well… let’s get into it!

The formation of high-altitude fallstreak clouds is a product of intricate atmospheric processes. Let’s delve into the step-by-step journey of how these captivating cloud formations come to life:

• Supercooled Water Droplets: Fallstreak clouds typically form in layers of altocumulus or cirrocumulus clouds that contain supercooled water droplets. Supercooled water remains in a liquid state even when its temperature drops below freezing, a critical factor in the formation of fallstreak clouds.
• Ice Nucleation: Under specific atmospheric conditions, supercooled water droplets can spontaneously freeze. This process is known as ice nucleation, and it marks the starting point for the creation of fallstreak clouds. Tiny ice crystals begin to form within the supercooled cloud layer. This can often happen after an airplane passes through the area. Supercooled water is extremely unstable and any agitation may lead to nucleation.
• Growth of Ice Crystals: Once ice crystals emerge, they rapidly grow and multiply. This growth process happens at the expense of the surrounding supercooled water droplets. As more water molecules freeze onto the ice crystals, they become larger and heavier.
• Formation of Fallstreak: As ice crystals continue to grow, they reach a point where they are too heavy for the surrounding air to support. Consequently, they start to fall from the cloud layer, creating a distinct hole or gap in the cloud deck. This is the defining feature of a fallstreak cloud.
• Virga: As the ice crystals descend, they often evaporate before reaching the Earth’s surface, giving rise to another phenomenon known as virga. Virga appears as wispy, streaky tails extending downward from the base of the fallstreak cloud toward the ground.

Fallstreak clouds, with their hole-punched appearance and radiant skies, serve as a testament to the complexity and beauty of our atmosphere. While they may not grace our skies every day, they remind us of the endless wonders of nature and the intricate processes governing meteorology. So, the next time you gaze up at the sky and spot a fallstreak cloud, take a moment to appreciate the remarkable science and artistry that come together to create these fleeting masterpieces in the heavens.