Clearing the air on severe thunderstorms

I was reading comments on social media relating to recent thunderstorm activity in Nova Scotia. There seemed to be a lot of confusion about what constitutes a severe thunderstorm and who’s at liberty to designate a thunderstorm as being severe.

Let me first start by saying the amount and intensity of lightning, or how loud the thunder is, does not determine whether a thunderstorm is severe or not. Regardless, lightning is extremely dangerous and can be deadly. That is why when thunder roars, go indoors.

A thunderstorm is designated severe when there is evidence on radar, satellite or from a reliable spotter that any one or more of the following three weather conditions is imminent or occurring: wind gusts of 90 km/h or greater, hail of two centimeters or larger in diameter, 25 mm of rain or more within one hour.

A severe thunderstorm watch will be issued if conditions are favourable for the development of thunderstorms that are capable of becoming severe. The watch is upgraded to a warning if severe storms are imminent or happening.

It’s important to note you can be placed under a severe thunderstorm watch but not be experiencing a severe thunderstorm.

Forecasters have the tools to predict severe weather through weather model data and then track it in real time through radar and satellite imagery.

But it’s key to remember Environment Canada decides whether a severe thunderstorm watch, or warning, is issued.

I also like to stress while weather modelling is great and continues to improve, it’s only a guide. Models have biases and cannot always interpret certain projections accurately.

Lastly, we all interpret thunderstorms and our weather in general differently. But it’s important to know the source of the information that’s being provided to you with severe weather events, especially on social media.