When it rains cats and dogs

Thunderstorms are the sort of meteorological events that attract more attention in the summer, especially in certain Canadian provinces, because they are the source of natural catastrophes that can do a great deal of damage.

What kinds of conditions create thunderstorms and what forms do they take?  Let’s have a look at thunderstorms in Canada.


Where do they occur?

The regions of Canada most affected by thunderstorms are the Prairies, southern Ontario and southern Quebec. The conditions there are ripe for storms from spring to the end of summer. The terrain is also a major factor in those areas, with the Rocky Mountains in western Alberta and the Great Lakes bordering Ontario. But apart from geography, what combination of factors causes storms?

A recipe for thunderstorms


The ingredients of a storm include moisture, heat, unstable air, and lift. Just as in baking, that mix of elements is what makes the cake rise or, in this case, makes the rain fall!

Lift can be caused by a cold front or by mountains, for example.

As the day progresses and the sun warms the air, there is a greater chance of upward lift. After all, hot air will rise!

The air is considered unstable when it rises by itself due to the sun rather than being forced upward by a front or a mountain. That’s why thunderstorms are more frequent in the late afternoon and early evening.

Moisture in the air condenses as it rises, forming a cloud. The more the air is drawn upward by the ongoing warming of the sun, the greater the chances that the thunderstorm will gather and grow stronger. A thunderstorm can be over in just 30 minutes, but a severe thunderstorm driven by heat and humidity can remain active for several hours.

The dangers stemming from thunderstorms



Hail consists of balls of ice that can range in size from that of a pea to a softball. Hail shouldn’t be mistaken for the sleet that falls in winter; it is typically a warm-weather phenomenon.

Hail forms when ice crystals in thunderstorm clouds mingle with water droplets that freeze on contact and grow larger. The stronger the storm, the more the updrafts sustain the hailstones, allowing them to grow.

Hail is most frequent and tends to be most severe in the region east of the Rockies. The worse the conditions – high humidity and high temperatures, for example – the more the hail can grow. And hail can cause real damage to buildings and cars. Here are preventing tips for hailstorms!

Heavy rain 

Heavy rain

Condensed moisture forms water droplets that eventually fall to the ground. The more moisture there is and the more sustained the lift, the more the cloud will be bursting with water. Since what goes up must come down, it means there is serious rain on the way.

In a thunderstorm, rain falls in a concentrated area, so it’s not rare for it to rain in Montreal with nary a drop falling in Laval.  Thunderstorms can cause flooding and sewer back-ups.



When ice particles collide inside clouds it produces an electrostatic discharge, like when you rub a rubber balloon against your hair. Lightning is how the cloud discharges electricity, sending it earthward.

When striking dry vegetation, lightning can start forest fires, or even house fires when striking electrical wires. More severe storms generate more lightning. Lightning can also flow between cloud layers and between clouds themselves.



Tornadoes are violent rotating winds that can destroy entire homes leaving only the foundations. The precise causes of tornadoes are not altogether clear, but they only occur in severe thunderstorms.

Tornadoes are infrequent in Canada, but they do happen in every province where thunderstorms occur. They can touch down in the middle of a forest where there are no people, so they are not always seen. The strongest tornadoes occur in the Prairie Provinces, followed by southern Ontario.

Damaging winds 

Damaging winds

Have you ever noticed that the wind rises just before a thunderstorm? That's because strong winds are caused by hot and humid air that became cool and dry after rising. Once the air has risen and transferred its humidity to the cloud, it returns to the ground and spreads outwards, producing winds.

The bigger and heavier the cloud, the greater the risk of violent winds with short sudden gusts strong enough to cause damage.


While thunderstorms can be a cause for concern, the cooler, drier weather after a thunderstorm can come as a welcome relief, especially after a heat wave!

The best way to avoid an insurance claim is, as always, prevention! Make sure that your house is in good repair — from the roof to the sump pump in the basement — so that it can withstand a thunderstorm and you can avoid water damage.

Have a good summer!