Moving toward Free-Form Threat Polygon Based Convective Warnings at the Meteorological Service of Canada

Currently, the Meteorological Service of Canada (MSC) uses county-based zones to reference areas under threat from meteorological hazards. However, the areal extent of convective weather events (thunderstorms and tornadoes) does not follow pre-defined boundaries. Consequently, county-based zones often over-reference the true area under threat.

While improvements to the warning decision process for MSC forecasters is ongoing, improvements to the client -facing convective warning product can still be made. The Convective Alert Modernization (CAM) project, initiated in early 2022, will modernize the production and delivery of convective weather warnings in Canada. The project aims to reduce the areal over-alerting of the risk associated to tornado and severe thunderstorm hazards by introducing forecaster defined free-form polygons to more precisely reference the boundaries of the predicted convective weather threat. This work will not only improve the tools that forecasters use to generate convective alerts, but also improve the timeliness and usability of service products available to Canadians.

Preliminary testing of the new alert production software during the summers of 2022 and 2023, shows promising results with a reduction in areal over-alerting and a design that accommodates an improved forecaster workflow. However, testing has highlighted nuanced dissemination issues that need to be addressed when updating free-form warnings in the Canadian context.

This presentation will introduce the CAM project and will highlight the development work underway, including challenges encountered, to introduce free-form polygon weather warnings that describe the risk with greater spatial and temporal precision. Additionally, this presentation will describe proposed changes to alerting practices made possible with this moving threat-based polygon paradigm.