A weather watch means that there is potential for the weather event to occur. No action needs to be taken when watches are issued, however residents should keep up to date in case the watch becomes a warning.
A weather warning means that the weather event is either imminent, or is currently occurring. This can be based on either doppler radar, or eyewitness accounts and residents should be prepared to take action.
A weather advisory also means that the weather event is either imminent or occurring, however, is less severe than a weather warning.