Weather 101: Hole Punch Clouds

I am excited to be contributing my library of Weather 101 stories to the blog. Look for a couple of them each week as we renew our commitment to Alabamians with the best weather information and other relevant content.
– Brian Peters

Photo courtesy of Tim Pigott ?(@Tdpigott). Captured on 29 Dec 2015 over Tuscaloosa.

I’ve never had the opportunity to see one in 50 years in the weather business, but I’ve seen pictures. The phenomenon of hole punch clouds is extremely fascinating. A hole punch cloud is sometimes called a fallstreak hole. These clouds can create some strange appearances in the sky that are often circular or oval and may be reported as UFOs.

What could create a huge hole in the clouds reminiscent of the movie ‘Independence Day’? Such a hole, likely hundreds of meters across, was photographed in late 2003 over the northern Gulf Coast near Mobile, Alabama, but have been observed in many other locations. Very unusual to see, hole-punch clouds are still a topic of some meteorological speculation.

The leading hypothesis suggests that hole-punch clouds are caused by falling ice-crystals. The ice-crystals may originate in a higher cloud or be created by the exhaust of passing airplane – a contrail. If the air has just the right temperature and moisture content, falling crystals will absorb water from the air and grow.

But for this to happen, the liquid water must exist at temperatures well below freezing – a condition called supercooled. In this environment, all the moisture needs is a surface to freeze on. Moisture lost from the air increases the evaporation rate from the cloud water droplets so they dissipate to form the hole or elongated circle. The now heavier ice crystals continue to fall and form wispy cloud-like virga seen inside and just below the hole. Water and ice from the virga evaporates before they reach the ground.

This is just another fascinating example of our atmosphere in action – and another reason to keep your eye skyward.

There’s not a cloud in the sky now so another day without a hole punch cloud! If you have a question about the weather, use the comment feature below and we will try to answer it!

Category: Met 101/Weather History