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CINDY DAY: Clearing the air about thunderstorms

This incredible photo was taken by Neil Green as a bolt of lightning lit up the sky on Brier Island, N.S.
This incredible photo was taken by Neil Green as a bolt of lightning lit up the sky on Brier Island, N.S. - Contributed

When I moved to Atlantic Canada 20 years ago, my co-workers told me that “we don’t get much heat here”. Well, this stretch of sultry summer weather reminds me of “Ontario heat”.

Growing up on a farm in southeastern Ontario, I’m very familiar with heat and humidity. The heat didn’t stop us from working but a break in the weather was usually welcome. Grandma used to say “a good thunderstorm will clear the air”. It often did, but not always. 

Here’s why:

Some of our most spectacular summertime thunderstorms develop along a boundary line that sits between two air masses: a very warm one and a much cooler, drier one. That line is a cold front.

Thunderstorms along a cold front “clear the air” because the wind turns to the west or north-west behind them and that circulation is, if not cooler, usually much drier or less humid. Rain also has the ability to wash dust particles from the sky.

These microscopic particles form a foundation for the condensation of water vapour, which disperses sunlight and can obscure visibility. After a good rain, the visibility often improves and the air feels cooler thanks to the cold air that rushes down from the top of thunderstorm cells.

However, if the thunderstorms were not created by lift along a cold frontal line, it can rain all it wants, but a few hours after the rain stops, you’re back to where you started. 

The showers and thundershowers that came through late Thursday were associated with a trough of low pressure: an extension from a low, and not a true cold front. The wind backed to the west for a very short time then settled again in the southwest.

That southwesterly circulation continues to pull warm, humid air into our region. A small wind-shift line will push through Sunday into Monday. Behind it, a light westerly breeze will offer up some relief from this very humid stretch of weather. 

I’m going to do what I can to enjoy the summer, heat or no heat. August is just days away and before long I’ll be dealing with complaints about the cold!

Cindy Day is the chief meteorologist for SaltWire Network.

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