Top News

The News

WEATHER U: No holes in this theory

David Blight and his son were surprised to see what looked like the beginning of a tornado over the Chain Lake area of Halifax last week.  However, things are not always as they appear! What they observed is a fallstreak.
David Blight and his son were surprised to see what looked like the beginning of a tornado over the Chain Lake area of Halifax last week. However, things are not always as they appear! What they observed is a fallstreak. - Contributed

I could stare up at the clouds all day. They can be fun, beautiful, colourful and, at times, frightening.

Earlier this month, David Blight was out with his son when they happened to notice an intriguing display – what looked like a hole in the cloud with a funnel, of sorts, reaching from its centre. David wanted to know if this might have been the beginnings of a tornado?

The photo shows a fairly rare cloud called a punch hole cloud or fallstreak hole. A fallstreak or punch hole is a large circular gap that can appear in the clouds, usually in cirrocumulus or altocumulus clouds. Those cloud layers can be made up of small water droplets that are below freezing but not frozen: super-cooled droplets. If ice crystals form in the layer of super-cooled droplets, they grow rapidly and shrink or even evaporate the water droplets completely. This is known as the Bergeron process. Studies have shown that aircraft passing through these cloud layers can trigger the formation of the heavier ice crystals, which fall to earth and then leave the circular void in the blanket of clouds.

As the fallstreak hole develops, cloud will appear in its centre but there is normally a clear “ring” around the outside. The cloud inside the fallstreak hole is often stringy and can look like a twisted braid. That’s why David thought he and his son might be witnessing the development of a tornado.

You won’t find any dangerous weather associated with this phenomenon; in fact, there is usually no weather at all.

These cool clouds have been around for a while. Scientists first reported observing punch hole clouds in the 1940s;the cloud sightings often lead to false reports of UFOs or rocket launches.



Cindy Day is the chief meteorologist for SaltWire Network.

Recent Stories