We usually got news about weather alerts from those public medias, but, most of weather alerts might be issued by Environment Canada.
For weather, they have a specified link: www.weatheroffice.gc.ca.
We can check the original alert content on their website.
Here is a sample, a latest alert for Toronto:
Alerts for: City of Toronto
City of Toronto
12:11 PM EST Saturday 04 January 2014
Special weather statement for
City of Toronto continued
Winter storm with heavy snow later Sunday and Sunday night, with mixed precipitation for some regions. Windy and sharply colder again Monday with some blowing snow and lake effect snowsqualls.
Here is Public Weather Alerts for Canada