Mods like MorrowLoot Ultimate change Skyrim's encounter zones so that enemies in a dungeon might start at level 20 instead of level 5. However, enemies directly outside that dungeon will typically scale with the player's level. This can mean radically different leveled enemies going from exterior to interior - you might have no trouble getting in but face a sudden spike of difficult when you head inside.

This script assigns encounter zones to worldspace cells based on their location. This also means that purely outdoor areas like Valtheim Towers can have their own level.

Installation/Usage
Make sure MXPF and outdoor zone-o-matic are in xEdit's Edit Scripts/ folder.
After loading your mods in xEdit, right click on any record, select Apply Script, select outdoor zone-o-matic and hit OK.
Enter whatever file name you want.
Exit, saving the new plugin.
Be sure to activate it before playing.

You can run the script again to update your plugin. It should stay near the bottom of your load order.

Should also work with non-Special Edition Skyrim. Should technically also work with Fallout 4, though FO4 already zones exteriors using a different method.

Notes
I don't think any of Skyrim's worldspace cells have encounter zones assigned to them. You're technically able to do this in the CK, though this seems to be through a bug. There's a remote chance there might be some weird behaviour, but it probably won't break your game!
Worldspace cells won't lock zone levels like interiors do.

thanks