Preliminary: Well, by definition it's "Done in preparation for something fuller or more important". It's a working advisory. Normally issued 3-4 days before said event and updated at least once every 6/8 hours. Areas can be cast wide and scaled down later.
Active: We'll move from Preliminary to Active 24 hours or less before said event. Normally this means we'll no longer update it but depends on the complex nature of the snow event.
Expired: The event has passed and the advisory is no longer in force. Our new system allows us to archive old advisories for anyone to look back on at a later date.
Withdrawn: Any advisory can be withdrawn, but usually it'll be of a Preliminary status that we have issued early but model guidance has changed and forced us to retreat.