Severe Summer Weather & Tornadoes


In Ontario, thunderstorms develop in a warm, humid, unstable air, most often between May and September.  Storms often only last up to an hour or so, but a line of thunderstorms can last for several hours.

Particularly severe thunderstorms are often accompanied by hail, frequent lightning, damaging winds, heavy rain and possibly tornadoes.  Tornadoes are often difficult to predict, which is why some Severe Thunderstorm Warnings include statements about the potential for tornadoes, even though a Tornado Watch or Warning hasn’t been issued.  During very strong thunderstorms with high winds, you should take shelter for safety, just as you should during Tornado Warnings.

Photo of a severe thunderstorm approaching.

Severe Thunderstorms

Environment Canada is responsible for issuing weather “Watches” and “Warnings“, which are terms that are easily confused…

A severe thunderstorm WATCH is issued when weather conditions are right for thunderstorms to develop later in the day.  Keep an eye on weather conditions where you are and listen for weather reports on the radio, a weather radio, or a reputable website such as Environment Canada.

A severe thunderstorm WARNING is issued for areas in the path of a storm that is causing heavy rain, hail or damaging winds.  Severe Thunderstorm Warnings sometimes include the risk of tornadoes, so be prepared to take shelter if threatening conditions exist.

When the sky looks threatening, turn on your radio and listen to weather reports, or go to the Environment Canada website for information.  Consider purchasing a weather radio, or subscribing to one of the weather alerting services available to the public.  If residents in your area are advised to take cover, do so immediately!

Lightning over a field

Lightning Safety

In Canada, lightning typically kills 10 people and injures 100 each year.  Lightning is extremely common and causes more deaths and injuries to Canadians than tornadoes.

During thunderstorms, the air is charged with electricity and this is seen as lightning.  Not all lightning reaches the ground, but when it does, electricity can flow to trees, water, rocks, buildings and people!

When there is thunder, there is always lightning (and vice versa)!  Sometimes, especially at night when lightning flashes are visible for long distances, you can see lightning, but not hear thunder.  This is often called “heat lightning“, but it’s really just lightning from a storm that is so far away that you can’t hear the thunder.

Taking Shelter

If you hear thunder, it means that lightning is close enough to strike you.  If you are indoors, stay there, but away from windows, doors, fireplaces, radiators, stoves and appliances.   Do not use telephones or computers unless they are wireless.  Do not take baths or showers.  Metal plumbing, wires and cables can conduct electricity from near-by lightning strikes.

lightning and barn 1There are no safe spots outdoors during a thunderstorm.  Quickly get inside a substantial building or a vehicle with a metal top.  If that isn’t possible, you need to find the best of the poor options available – try to find a low area such as a ditch, a valley, or a very dense grove of trees, but never take shelter under a solitary tree.

Tents, picnic shelters, gazebos, barns and drive sheds do not provide adequate protection from lightning – get inside a more substantial building or a vehicle.  If you are swimming or boating (especially in a boat without lightning protection), get to shore immediately.

If you are in a vehicle, pull away from trees and hydro poles that might fall on you.  Do not touch any metal parts inside the vehicle (it’s the metal body surrounding you that protects you from lightning, not the rubber tires).

“When the sky roars, get indoors!”

Environment Canada recommends, “If you can hear thunder, seek your best shelter immediately and remain in that shelter for a full 30 minutes after the last thunder to ensure the storm has moved off.  Or more simply put, “When the sky roars, get indoors” – and remain there for a full 30 minutes after the last rumble of thunder.”

Tornadoes | Tornado Touch Down


A tornado is a column of rotating wind, travelling across the land at up to 100 km/h.  Wind speeds within a tornado can range from 64 km/h to over 500 km/h.  Tornadoes can last minutes or hours.

Most tornadoes in Ontario occur from May to September in late afternoon and are most frequent during high summer temperatures, accompanied by high humidity.  On average, there are about 12 tornadoes in the Province each year.

Several significant tornadoes have touched down in Lambton over the years.  The most destructive tornado to date was an F3 tornado that crossed the St. Clair River and struck downtown Sarnia in 1953.  Other tornadoes include the 1983 Reece’s Corners Tornado (F3), the 2011 Central Lambton Tornado (F2) and the 2014 Grand Bend Tornado (EF1).

Click here to read more about these past tornadoes.

Tornadoes - Grand Bend Tornado PathThe photo on the left was taken by Lambton Shores Mayor Bill Weber, from a helicopter conducting an aerial damage assessment following the Grand Bend Tornado.  The tornado came in off Lake Huron as a strong storm cell on Sunday, July 27, 2014.

The tornado blew down thousands of trees and damaged a number of homes.  Since the photo was taken shortly after the tornado, the downed trees are still relatively green.  The light sandy soils exposed by the downed trees however, show the tornado’s path from the bottom of photo toward the dwelling with the red roof.

Tornado Warning Signs

Although there are often tell-take signs before tornadoes form, there are many, many instances of tornadoes forming unexpectedly, leaving no time for official warnings or for people to take shelter.  There are however, stories of people taking shelter and saving themselves simply because they thought the sky looked strange or had a feeling that something wasn’t right.  If weather conditions or the appearance of the sky causes you concern, do not wait for a warning – be safe and take shelter.  The following conditions could precede a tornado:

  • Thunderstorms that grow steadily worse, with heavy rain and extreme thunder and lightning.
  • Large hail (hail larger than a nickel is evidence of a strong storm).
  • An extremely dark sky, sometimes highlighted by rotating green or yellow clouds.  Sometimes wisps of cloud will be seen swirling upward toward a low point in the clouds.
  • An eerie calm at the end of a severe storm – the sun might even be visible.
  • A rumbling sound like a freight train, or a whistling sound like a jet.
  • A “wall of white” coming toward you – many tornadoes are hidden by heavy rain and a funnel might not be visible.

If you observe any of the above warning signs, take cover immediately!

Tornado Facts

  • Most tornadoes are less than a few hundred metres across, but the 2013 El Reno Oklahoma Tornado reached a width of 4.2 kms (about 2.6 miles) – the widest tornado ever recorded.
  • Most tornadoes form near the south-west end of a storm, just when conditions seem to be improving.  In fact, the sky may already be brightening in the distance.
  • The air may be unusually calm just a few kilometres away from an active tornado.  However, it is dangerous to be outside near a tornado because pieces of debris drawn into the storm can fall from the sky without warning.
  • Some people have compared the sound of a tornado to a jet engine or a freight train, but some tornadoes produce no sound.  Irregular crashing sounds could be from damage being caused by the tornado.
  • Do not assume that you will see or hear a tornado coming.  Tornadoes do not always have visible funnels and heavy rain often hides tornadoes.

Be Aware & Be Prepared: Watches & Warnings

Environment Canada will issue tornado Watches or Warnings when necessary, but tornadoes can form unexpectedly, so a Watch or a Warning might not precede a tornado touchdown.  Warnings will typically be announced by Environment Canada over local radio and television stations.  There are significant differences between Watches and Warnings:

A Tornado WATCH may be issued when conditions are favourable for tornadoes to develop later in the day.  This is a significant weather development, so monitor weather conditions and listen for updated weather reports.  Be prepared to take action if severe weather develops.

A Tornado WARNING may be issued when a tornado has been sighted, or if radar detects storm rotation.  Residents in the area covered by a Warning will be advised to take shelter immediately!

When weather conditions look threatening, turn on your battery-powered radio and listen for weather reports or check the Environment Canada Warnings webpage.  If residents in your area are advised to take cover, do so immediately.

What To Do When A Tornado Threatens

  • Take shelter immediately, preferably in the lowest level of a sturdy building.
  • Stay away from windows and exterior doors and walls. Flying glass and debris blown into a building are extremely dangerous.
  • Do not spend valuable time opening windows to prevent your home from “exploding.”  Buildings are typically damaged by wind and blowing debris – not by a sudden drop in air pressure.  In fact, when a Tornado Watch (see above) is issued, you should close any open windows, doors and garage doors.  Winds can enter building openings (especially though open garages) and cause walls to blow out and roofs to collapse.
  • Take cover immediately when advised or when conditions are threatening.

Finding Shelter

  • In a house, go to the basement and take shelter under a stairway or a sturdy piece of furniture such as a table.
  • In a house with no basement, go to a closet or a bathroom near the centre of the building, without windows. Lying in a bathtub with a mattress on top may provide additional protection.
  • In a large building such as a grocery store or shopping mall, go to an interior hallway or a washroom on the lowest level, or get under a sturdy piece of furniture.  Avoid large, open areas and stay away from windows.
  • In high-rise buildings, go to the lowest level, a small interior room or a stairwell.  Stay out of elevators and away from windows.
  • If you are camping, hiking, biking or outdoors when a tornado is approaching, and there are no good shelters nearby, your situation is dire.  Try to find a low-lying area such as a ditch and get into it.  If there are no low areas, try to get deep into a thick cluster of trees and get down as low as possible.  Protect your head from flying debris – small objects can become lethal projectiles when driven by tornadic winds.
  • If you are driving and see a tornado in the distance, try to determine what direction it is heading and get out of its path if possible.  If it is not possible to escape the tornado, find shelter.  Do not take shelter under an overpass.  If the tornado is approaching, get out of your vehicle and take cover in a low-lying area.  If no good shelter is available, and debris is flying, your only option may be to park at the side of the road, leave your seatbelt on and get below the level of the windows.  A strong tornado can easily toss or carry even large vehicles, but when absolutely no other shelter exists, your vehicle might provide some protection.   Note that if a tornado seems to be standing still, it is likely either travelling away from you, or heading right toward you!

The Enhanced Fujita Scale

On April 1, 2013, Environment Canada’s Weather Service introduced a new scale to measure the intensity of wind damage. This scale, called the Enhanced Fujita Scale or EF-Scale, is a more modern and improved version of the original Fujita Scale (F-Scale).

As with the original scale, the EF-Scale is a 6-point scale that goes from zero (weakest) to five (strongest).  Its adoption unifies the approach to wind damage assessment in Canada and the United States, which adopted the enhanced scale in 2007 (all Canadian tornado examples provided below and prior to 2013 were assessed on the original F-Scale).

EF0 – light winds of 90 to 130 km/hr; some damage to chimneys, TV antennas, roof shingles, trees, signs, and windows.  EF0 tornadoes account for about 28 percent of all tornadoes.

EF1 – moderate winds of 135 to 175 km/hr; automobiles overturned, carports destroyed, and trees uprooted.  EF1 tornadoes account for about 24 percent of all tornadoes (i.e. 2014 Grand Bend Tornado).

EF2 – considerable winds of 180 to 220 km/hr; roofs blown off homes.  Sheds and outbuildings demolished, and mobile homes overturned.  EF2 tornadoes account for about 24 percent of all tornadoes (i.e. 2011 Central Lambton Tornado).

EF3 – severe winds of 225 to 265 km/hr; exterior walls and roofs blown off homes, metal buildings collapsed or severely damaged, and forests and farmland flattened.  EF3 tornadoes account for about six percent of all tornadoes (i.e. 1953 Sarnia Tornado and 1983 Reece’s Corners Tornado).

EF4 – devastating winds of 270 to 310 km/hr; few walls, if any, left standing in well-built homes.  Large steel and concrete objects carried or thrown great distances. EF4 tornadoes account for about two percent of all tornadoes (i.e. 1946 Windsor Tornado and 1985 Barrie Tornado).

EF5 – incredible winds of over 315 km/hr causing total destruction; well-built homes swept away and obliterated, asphalt scoured from roads, vehicles carried great distances and ripped apart.  EF5 tornadoes can cause tremendous or complete damage to most buildings and structures.  Tornadoes of this magnitude account for less than one percent of all tornadoes.

Many people think EF5 tornadoes only occur in the central U.S. “Tornado Alley”, but in 1953 a devastating F5 tornado struck within 110 km of Lambton County near the City of Flint, Michigan.  Another F5 tornado hit Michigan in 1956 – this time in the Grand Rapids area.  There has been only one documented F5 in Canada, which occurred in Elie Manitoba on June 22, 2007.

Tornadoes - F3 Sarnia 1953
Sarnia F3 Tornado damage looking south on Front Street, May 1953.
Tornadoes - F4 Windsor 1947
The F4 Windsor Tornado of June 1947, which killed 17 people.