There are three types of weather alerts:
Special weather statements are issued for weather events that are unusual, cause general inconvenience or public concern, and cannot adequately be described in a weather forecast.
Watches are issued when conditions exist that are favourable for a possible summer or winter storm. The storm could affect safety at at the very least will cause an inconvenience. In the summer a watch is issued up to 6 hours before a storm. In the winter, a watch can be issued up to 12-24 hours in advance. A watch can be upgraded to a warning.
Warnings are issued when severe weather is occurring or will occur. Severe summer storm warnings, such as thunderstorms, can be issued less than 1 hour in advance of the storm. Updates are issued as needed. Warnings should be taken seriously. When a warning is issued you should seek shelter and prepare to activate your emergency plan.