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OTTAWA — Canadians are set to receive more precise tornado and severe thunderstorm warnings beginning Tuesday as Environment and Climate Change Canada moves away from alerts based on predetermined geographic regions.
The new system will allow meteorologists to draw warning areas around individual storms and their projected paths, reducing the number of people receiving emergency notifications for severe weather unlikely to affect them.
The targeted areas, known as free-form polygons, will be used for tornado and severe thunderstorm warnings. Watches and other types of weather alerts will continue to use existing geographic zones.
Under the previous system, warnings were issued across predetermined regions, some stretching hundreds of kilometres. As a result, people far from a dangerous storm could receive the same warning as those directly in its path.
With the new system, forecasters will draw a polygon beginning around the location of the storm and extending in the direction it is expected to travel. The warning area will widen farther along the projected path to account for uncertainty in the storm’s movement.
Warnings will include information on the storm’s location, direction and speed, along with communities potentially in its path and hazards such as damaging winds, large hail or heavy rain.
The biggest change for many Canadians is expected to involve emergency alerts sent to cellphones.
When a tornado warning or qualifying severe thunderstorm warning triggers the National Public Alerting System, alerts will be directed primarily through cell towers serving areas within or immediately surrounding the warning polygon.
The change is intended to reduce unnecessary notifications and the risk of people becoming desensitized to repeated warnings for storms posing no immediate threat to their location.
Environment Canada has said the new system should also allow warnings to be issued more quickly and adjusted as storms move or change direction.
Similar storm-based warning polygons have been used in the United States for nearly two decades.
The Canadian system, known as Convective Alert Modernization, has been under development for several years. Tuesday is the planned launch date, although Environment Canada has indicated severe weather or technical issues could delay implementation, with Wednesday and Thursday serving as potential backup dates.
The change comes during an active severe weather season in parts of the Prairies, including Alberta and Saskatchewan, where tornado activity has been elevated this year.
The federal government has made several changes to Canada’s weather warning infrastructure in recent years, including completing an upgraded weather radar network and introducing a colour-coded alert system.
The new radar network scans the atmosphere every six minutes, compared with every 10 minutes under the previous technology.
Environment Canada’s website will display the new polygon warning areas and allow multiple warnings and watches to overlap on its maps.
The change applies only to warnings. Severe thunderstorm and tornado watches, which indicate conditions are favourable for severe weather to develop, will continue to cover broader geographic areas.
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