WeatherUnderground is using Mapbox as a service provider for their maps. It may take weeks, months or however long they are usually refreshing their data from OpenStreetMap. You will have to report it to WeatherUnderground or Mapbox as there is nothing that can be done here to update their data. Once it's changed here, there is nothing holding it back from being updated. It's on their end.

Thanks for updating it here.