Hi,
When you go through a location and it is registered as "My Location", or when you manually add a location, it will get registered for alerts, but it should be removed from the list not too long after you leave the location and My Location changes to a different locale or after the location is deleted.
If this does not occur, launch 1Weather and tap the menu and go to settings, Notifications, and un-check severe weather alerts.
Wait 3-5 minutes, then re-check severe weather alerts.
Every time you add a location, remove a location or turn notifications off, then back on the app deregisters/reregisters all of your locations.