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Why thunderstorms don’t always clear the air

ALLISTER AALDERS weather@saltwire.com @allistercanada Allister Aalders is the weather specialist for the SaltWire Network, providing forecasts and analysis for Atlantic Canada. #AskAllister

“We need a good thunderstorm.”

I hear this often during summer periods of high heat and humidity.

It’s often said a good thunderstorm will clear the air, helping break the humidity and cool things down.

While thunderstorms can provide relief from hot and humid weather, it’s not always the case.

Visualize this: If you cut a towering cumulonimbus thunderstorm cloud in half, you would see an updraft and a downdraft. The updraft is warm, moist air that rises and condenses, while the rainfilled downdraft brings cooler air to the surface.

That downdraft often results in a temperature drop for the location experiencing the storm.

But that drop is often temporary or doesn’t bring much relief elsewhere.

So, why don’t thunderstorms always clear the air? It’s often due to cold fronts. A cold front is one of the main triggers for thunderstorms as it forces the warm, humid airmass to rise over the cooler, drier airmass, often triggering thunderstorms.

A strong cold front can help change the flow of the atmospheric circulation, often flipping the wind direction to the west or northwest and allowing drier air to fill in behind it.

However, suppose the cold front is relatively weak. In that case, relief might only come for a couple of hours to a day before the dominant circulation pattern returns.

Single-cell thunderstorms formed from instability won’t cause a big change either since they are not associated with larger-scale changes in atmospheric circulation.

So, while yes, thunderstorms can clear the air, they don’t always.

It often takes a strong cold front to do so.

WEATHER

en-ca

2022-08-10T07:00:00.0000000Z

2022-08-10T07:00:00.0000000Z

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