New severe thunderstorm and tornado warnings for Canada

Lightning strikes from a severe warned thunderstorm in eastern Ontario. (Valley Weather Photo)

Environment and Climate Change Canada (ECCC) along with the Meteorological Service of Canada (MSC) has finally introduced the new polygon warning system across Canada as of this past Monday. The long awaited update follows a similar system that has been used across the United States for over 20 years.

In the past when a severe thunderstorm or tornado warning was issued, it would cover an entire geographically designated watch region, usually related to a County, Regional Municipality or city, as in the case of the Island of Montreal. Very often when a severe thunderstorm warning was issued for Montreal, only a small portion of the city would be impacted, leaving the rest of the population with fair skies. This created significant trust issue with the system.

As someone who has followed the weather for 50 years, this would often leave residents confused, and quickly loosing confidence in the weather office. The real threat here would be that the next time, the warnings could be ignored at terrible cost. As our climate changes across Canada, this type of approach to warnings was badly needed.

A sample of the new polygon thunderstorm warning. Forecasters will be able to precisely target those communities, regions or parts of cities that will be directly impacted by the advancing thunderstorm or tornado. Those warnings will then be pushed out by Alert Ready and the WeatherCan app for only those residents who are in the path of thee storm. (ECCC)

With the new polygon system, forecasters will target areas impacted directly by the approaching storms. The polygons will change quickly as the storms and the threats move along. Thunderstorms and tornadoes are often small in scale and impact very precise regions or neighbourhoods. The hope is that this will regain the public trust in the warning system with fewer "false alarms" being sent out over our cell phones through Alert Ready and on the WeatherCan App. This will also allow forecasters to update and advance the warnings more quickly to those who are in immediate danger from the moving thunderstorm or tornado.

The polygon system will only be used for thunderstorm and tornado warnings. Other weather warnings, and watches will continue to use the current traditional county and municipal alert boundaries.

The Polygon Warning System works!

So on the afternoon of Wednesday, August 12, when severe thunderstorms were impacting primarily extreme eastern Ontario into far western Quebec, Ile Perrot and Vaudreuil-Dorion, those areas were the only regions that received the thunderstorm warnings. The system worked! The storm dumped 25mm (1 inch) of rain at my weather station on Ile Perrot in under 1 hour, while only 1.4mm fell at Trudeau Airport in Dorval during the same period.