NOAA Radar Pro app allows you to add multiple locations in a variety of ways.
You can add location if you simply tap the screen in necessary place -- this will drop a red pin on it:
Tap the ">" button next to the locations name to see the detailed weather screen:
After this tap symbol in the top right hand corner in order to add location to the list of saved locations.
Alternatively, you might consider to add location directly to the list.
For this -- tap "Locations list" button in the low right corner of the app's main screen and then, on the next screen, tap + button:
On the next screen -- enter location's name in the search bar. After this -- tap one of the suggested variants in order to add it in the list. This will also drop a blue pin on the map.
This will add location to the list and drop a blue pin on a map.