Tuesday, June 18, 2013
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The afternoon calm slowly breaks as the rumble of thunder echoes in the distance. High level clouds begin to move in and a light breeze passes the area. The sky darkens, the winds pick up and heavy rain, wind, lightning and even hail and tornadoes erupt. A thunderstorm is here. This section looks at 5 main threats from thunderstorms; wind, hail, lightning, flooding and tornadoes with safety tips to keep you safe, explores some interesting facts on them, and explains how Environment Canada tracks these systems and issues statements to keep you informed.
Thunderstorms can happen anywhere and at anytime although the majority of them happen from April to October and usually in the early morning or late afternoon. There a many threats that thunderstorms have to people and property including tornadoes and large hail in large severe systems.
Strong winds are often associated with thunderstorms. In regular thunderstorms, winds may gust from 50 to 90 km/h. This will cause small branches to break, topple garden and lawn furniture and generally move things around that are not protected or tied down. In severe thunderstorms, winds may gust to 140 km/h or higher. This will cause large branches to break, outdoor furniture to be pick up and moved, and even move vehicles on the road. In many cases, roof damage and building damage have been reported.
If strong winds are
forecasted with thunderstorms, prepare to get inside immediately. Stay inside with doors and windows shut and stay away of
Each year in Canada, lightning kills an average of 16 people and causes more than 20 per cent of all forest fires (40 per cent in British Columbia.) Lightning also starts about 2000 fires annually on private property (about 2.5 per cent of all recorded fires.) You have a one in 350 000 chance of being killed by lightning; your chances of being killed in a car accident are 50 times greater.
If you are inside, close windows and doors and keep away from them. Don't go outside unless necessary. Before storm hits, unplug all appliances including TV, computer and don't touch electrical items or the telephone. Do not take a bath or use the faucets (the metal and water conduct it). If you are outside, Get inside building or vehicle if possible. Avoid water and objects that conduct water (tractor, golf clubs, etc.) Do not stay in open spaces or under tall objects (trees, poles). If no shelter available, crouch down, feet close together with head tucked down. If in a group spread out. Remember, lightning victims can be revived with CPR even when there is no pulse. Stay inside vehicle with windows closed and be wary of downed power lines that may hit your car. If this happens, stay there, the minute you jump out you may receive a shock. Avoid touching metal parts of the car. Do not drive - wait. But don't park under trees or large items as they may fall on your vehicle if hit.
Sudden cloudbursts can cause flash floods in creeks, ravines and streets, and can wash out or submerge culverts and bridges. As much as 5 cm of rain may fall in less than half an hour. In one case, rainfall amounts to 200 mm fell to the area around Punkeydoodle's Corners, SW of Kitchener in under 3 hours on July 14, 1997 causing severe flooding conditions.
If house located in low lying area, be prepared to move to higher ground at any time a watch is issued. If you are outside, do not walk through flash floods or flooded roads, paths. Waters may have washed out several feet below. If you are in a car/RV, avoid driving through flooded areas. If stuck, watch for road washouts and avoid underpasses, valleys. It may look like there is only a little water is running over the roads but it may be eroded many feet down.
Hail is formed when updrafts in thunderclouds carry raindrops upward into extremely cold areas of the atmosphere, where they freeze and merge into lumps of ice. When the lumps become too heavy to be supported by the updraft, they fall to the ground at high speeds. Just think, a 2.5 cm hailstone has a freefall velocity of 80 km/h. More information on this is here.
If you are inside, stay away from windows and glass doors. If you are outside, seek cover, face away from wind and protect your head. If you are in a car/RV, keep head and face away from windows. Large hail will shattered windows. In all cases, Be alert for high winds or tornado (especially if hail is large) and follow tornado advice.
Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere. Rising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical. An area of rotation, 4-10 kms wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.
If you are inside, Stay inside with doors and windows shut and stay away of these windows and exterior walls. Go to small interior room or stairwell on lowest floor of building (bathrooms are often best). If available, crouch under large/heavy furniture. Protect your head with cushion/mattress. If you are outside, seek shelter in building (not car/RV) immediately. If none available, lie flat in low dry spot (ravine/ditch) or under low bridge Keep alert of flooding. As a last resort, hang on tightly to the base of a shrub or small tree. If you are in a car/RV, do not stay in vehicle and do not drive to outrun it. Most people actually drive into the path. If, possible, run to nearby solid building. If none available, lie flat in ditch/ ravine and watch for flooding. Protect your head. Do not go under bridge overpasses, they are not safe locations as winds funnel into these areas and off little protection.
Thunderstorm detection at Environment Canada
Weather radar is a prime tool of Environment Canada in detecting heavy precipitation, rapidly developing cloud systems, and other signatures of severe thunderstorms. The radar beams picks up reflections in the atmosphere and returns them for the meteorologist to interpret. Satellites are also used to find thunderstorms in areas where radar is not present and can show the overall patterns and lifecycle of a thunderstorm system. In addition to technology, volunteer weather watchers scan the sky and report conditions to Environment Canada to help them assess the situation. When conditions are favorable for thunderstorms or severe thunderstorms are present, watches/warnings are issued by Environment Canada. These messages can be relayed to you via media outlets like TV, radio, internet or by weather radio which monitors weather radio bands and alerts you if warnings are present. A detailed look on specific watches and warnings are located here.
Weather Radio & CANWARN by Environment Canada
Weather radio is the first line in weather safety for the entire family to keep you informed of changing weather conditions. The weather radio is a unit that monitors a specific radio band produced by Environment Canada. If a watch or warning is issued for your county, it emits an alert tone that is loud enough to be heard within a house. This tone will continue until it is acknowledged or 2 mins has past. Then the message can be heard. It is your true 24 hour radio station for weather forecasts and information. I consider it as important as a smoke alarm as it has a battery backup so that information can still be received if the power goes out. More information on the weather Radio Alert System is available here. Weather Radios can be bought at Radio Shack online or in the store.
Canwarn is a volunteer organization of ham radio operators who report severe weather when they see it to Environment Canada. What they do is called ground-truthing. They confirm on the ground what satellites and radars see in the atmosphere. In addition, there are additional weather watchers that report to Environment Canada directly about weather conditions in the region including severe weather. Information on Canwarn is here. Contact your local Environment Canada office regarding Weather Watcher Programs in your area.
About 44 000 thunderstorms happen every day worldwide on average and produce 100 lightning flashes per second.
The Ontario Weather Page