|Severe weather is one of the major risks to the well being of citizens in the London area. Four of nine risks facing our City relate to severe weather.
Forecasting in this region is more difficult because of the lake effects, however prediction and warning technologies have improved immensely. It is important that the community use these improvements wisely to be better prepared for weather related events.
There are two main categories of weather risk that have to be considered: Summer and Winter. The key differences between these seasons are the types of mitigation and preparedness activities that can be used to protect life safety, and even reduce the property damage of severe weather.
Be Weather Aware!
It is important to consider the potential for severe weather when you are planning your daily activities. Take steps to keep you and your family safe when there is a chance that severe weather will strike.
Be sure you know the differences between weather advisories, watches and warnings.
Weather Advisory means actual or expected weather conditions may cause general inconvenience or concern, but do not pose a serious enough threat to warrant a weather warning. An advisory may also be used when conditions show signs of becoming favourable for severe weather when the situation is not definite enough or too far in the future to justify a warning.
Weather Watch alerts you that conditions are favourable for the development of severe weather. Watch the skies and listen for updated watches and possibly weather warnings.
Weather Warning alerts you that severe weather is occurring or that hazardous weather is highly probable. Severe thunderstorm or tornado warnings may be issued less than one hour in advance. Other weather warnings may be issued six to twelve hours in advance.
For the safety of people and property, Environment Canada issues severe weather warnings and watches and advisories to the public via the media, weather outlets and
Weatheradio Canada. Learn about the different types of watches and warnings at this Environment Canada website.
Make your plans accordingly -- know what to do before you need to do it! Check Environment Canada's
site for their
Tips on Preparing for Summer Severe Weather.
Summer Severe Weather
Summer weather, has a tendency to be more volatile and, to a certain extent, less predictable in terms of lead time for preparedness. This is especially true for Pulse thunderstorms and Lake Breeze Convergence that are common factors in our region..
A Severe Thunderstorm Watch is issued when conditions are likely for the development of thunderstorms, some of which may become severe thunderstorms with large hail, heavy rain, deadly lightning or damaging winds and possibly tornadoes within the areas and times specified in the watch. You should use this time to secure loose objects, shelter animals, ensure family members or co-workers are prepared to take action and listen carefully for an updated weather report. This is the time to develop a plan.
A Severe Thunderstorm Warning is issued when a severe storm has developed, producing one or more of the following conditions: flooding rain, destructive winds with gusts greater that 90 km/h, hail of at least 10 to 20 mm in diameter or intense lightning. Severe thunderstorms may also produce tornadoes. The storm's expected motion and developments will be given in the warning. If you are in the area specified, take shelter.
A Tornado Watch is issued when severe thunderstorms have developed and there is the possibility of one or more tornadoes developing within the areas and times specified in the watch. Be prepared to take action if a warning is issued.
A Tornado Warning is issued when one or more tornadoes are occurring in the area specified or detected on Doppler radar. The expected motion, development and duration will be given in the warning.
Many people mistakenly think that a highway overpass provides safety from
a tornado. In reality, an overpass may be one of the worst places to seek
shelter from a tornado. Seeking shelter under an overpass puts you at
greater risk of being killed or seriously injured by flying debris from the
powerful tornadic winds. Check the U.S. National Weather Services' advice on
Rain that is particularly heavy can cause traffic disruption, flooding and landslips, drainage and sewer problems and potential water contamination from runoff or in flooded areas. A Rainfall Warning is issued when heavy or prolonged rainfall is sufficient to cause local or widespread flooding or flash floods. Ensure drainage systems are clear of debris and operating. If travelling, give yourself extra time since sections of road may be flooded and driving conditions may be treacherous, especially in a low-lying or mountainous areas.
Local rainfall thresholds vary considerably across Canada and reflect a potential for regional flooding. Some seasonal considerations are made for ground that is frozen or sodden.
A rainfall warning is generally issued not more than 24 hours in advance and is not preceded by a watch.
Environment Canada has some excellent information available in Adobe Acrobat format:
Winter Severe Weather
Winter weather is somewhat more predictable for weather systems moving through the area and allows for much better lead time.
However, lake effects can mean inconsistent precipitation (i.e., part of the city gets a larger amount of snow than another) or a lake effect squall remains stationary over our area and delivers a large amount of snow when no system is in the area. This type of streamer effect can cause sudden, almost zero visibility on highways.