New targeted warnings for severe thunderstorms and tornadoes

Environment and Climate Change Canada is changing how we issue severe thunderstorm and tornado warnings.

Environment and Climate Change Canada is changing how we issue severe thunderstorm and tornado warnings.

Our forecasters can now target the area most likely to experience the highest impacts and issue severe thunderstorm and tornado warnings to people in only that area. Forecasters identify these targeted areas by drawing a shape around them called a ‘polygon’.

As the storm system moves, forecasters can update the polygon, triggering alert notifications along its route.

Figure 1: A targeted severe thunderstorm warning polygon can be seen over radar images of an active storm system, as it would appear on the Weather Information Map found on Canada.ca/weather.

Many predetermined alert zones are large and geographically spread out, meaning a weather alert that affects one part of a zone may not affect another. Targeted warnings mean that people who receive an alert are more likely to experience impacts.

Figure 2: A severe thunderstorm warning issued to the pre-determined alert zone over the same storm system as Figure 1. This image highlights the contrast between targeted warnings and broader alert zones.

All other types of weather alerts (for example, rain or heat) will continue to be issued to the broader pre-determined alert zones, including severe thunderstorm and tornado watches.

Implementing polygons is a major technical undertaking. Because of this, we are incorporating them into our alert system gradually. We are applying them first to severe thunderstorms and tornadoes, as these hazards benefit the most from using polygons because they tend to be more localized compared to other types of alerts.

Our forecasters can now issue severe thunderstorm and tornado warnings faster than ever before, thanks to improved tools coupled with more streamlined processes.