Weather Warning Index
When severe weather threatens, Environment Canada issues weather warning bulletins that notify those in affected areas so that they can take steps to protect themselves and their property from harm. Each year, the Meteorological Service of Canada issues, on average, 15 000 severe weather warnings. A weather warning is an urgent message that severe weather is either occurring or will occur. Warnings are usually issued 6 to 24 hours in advance, although some severe weather (such as thunderstorms and tornadoes) can occur rapidly, with less than a half hour’s notice.
The Weather Warning Index (WWI) was created to track the performance of Environment Canada’s severe weather warning system in providing Canadians with warnings in sufficient lead time.
The WWI score for the three-year period 2009–2011 was calculated to be 7.5 on a maximum scale of 10. Since this is the first time that this index is being reported, no trend analysis is possible.
Weather Warning Index for a three-year moving average, 2009–2010–2011
Note: The index reaches 10 if all extreme weather events in targeted areas were preceded by a warning with sufficient lead time, as per the weather warning performance targets.
Source: Performance Management Division, Environment Canada (2012).
The WWI is calculated based on information from six warning types that are representative of Canada’s climate. These warning types are severe thunderstorm, rainfall, freezing rain, wind, snowfall, and marine gale. For each warning type, a component score is determined based on the warning's accuracy in predicting an actual severe weather event and its timeliness in comparison to the lead times identified within Environment Canada warning performance targets.
The WWI components are calculated using warnings data from a set of selected geographical regions considered representative of the Canadian climate and for which Environment Canada has sufficient warning events information.
The components are an indication of Environment Canada’s performance in providing timely and accurate warnings for each warning type. For instance, the score for Severe Thunderstorm highlights the challenge of forecasting severe thunderstorms in a timely and accurate manner when compared to other types of severe weather.
| Warning Type | Rain | Snow | Freezing Rain | Wind | Severe Thunderstorm | Marine Gale |
|---|---|---|---|---|---|---|
| WWI score | 8.0 | 7.3 | 7.1 | 8.7 | 4.9 | 8.3 |
Note: The index reaches 10 if all extreme weather events in targeted areas were preceded by a warning with sufficient lead time, as per the weather warning performance targets.
Source: Performance Management Division, Environment Canada (2012).
Environment Canada’s national weather forecast and warning system relies on several observation networks to detect changes in the atmosphere and the development of threatening conditions. The monitoring infrastructure includes 31 weather radars, 84 lightning detection sensors, approximately 1300 surface weather and climate stations, 70 weather buoys, 56 automated ship observation programs and 31 stations for launching balloon-borne observations of the upper atmosphere. Also extremely valuable to Environment Canada are hundreds of volunteer weather observers and severe weather watchers from coast to coast.
Weather warnings are invaluable for the protection of life and property and critical to provincial and municipal emergency measure organizations for managing flood control, sewer overflow and stormwater run-off. Weather warnings are also critical for weather-sensitive users such as snow removal operators and outdoor recreational enthusiasts.
Related information
Environment Canada - Hazardous Weather
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