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WEATHER U: The science behind stormy skies

Jordy Leighton lives on Grand Manan Island, N.B.  He was out just before sunset Wednesday and couldn’t help but reach for this phone and snap photos of the ominous sky.
Jordy Leighton lives on Grand Manan Island, N.B. He was out just before sunset Wednesday and couldn’t help but reach for this phone and snap photos of the ominous sky. - Contributed

I’d like to begin by thanking my many Facebook friends for taking time to post such fabulous photos. If you don’t follow me on Facebook, you don’t know what you’re missing. It’s a fan page, so just “like” one of my posts, and we’re friends.

Last week, I came across a series of dramatic photos taken by Jordy Leighton. Jordy lives on Grand Manan Island, N.B. He was out just before sunset Wednesday and couldn’t help but reach for this phone and snap photos of the ominous sky.

Jordy wants to know what was going on…

Well Jordy, last Wednesday evening a cold front was moving across the region. As the colder air gushed down, it created a gust front that caught your attention.

A gust front is the leading edge of cool air rushing down and out from a thunderstorm. The swirling effect of cold air pushing down and the warm air rising above it can produce an ominous-looking shelf cloud.

So what causes the air to flow out of some thunderstorms so rapidly?

The primary reason is the presence of low humidity in the lower atmosphere. This dry air causes some of the rain falling through it to evaporate which, in turn, cools the air. Since cool air is heavier than warm air, it sinks, and this causes a down-rush of air that spreads out at the ground. The edge of the rapidly spreading pool of cool air is the gust front.

If the wind following the gust front is intense and damaging, the windstorm is known as a downburst.

Thanks for being curious Jordy; I hope this answers your question.

I was blessed with many great teachers over the years. I remember my grade 11 biology teacher saying: “If you don’t ask, how will you know?”

I’ve never forgotten that.



Cindy Day is the chief meteorologist for SaltWire Network.


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