"IBM purchased the Weather Co. in 2016 and sells weather data to, among others, Apple, for its weather app. The purchase could signal that Apple will develop its own weather model rather than continue to use IBM-derived data, or it may indicate that Apple, too, liked the design of the app." https://www.washingtonpost.com/weather/2020/03/31/apple-buys...
It's turtles all the way down[1]. The Weather Company also leverages NOAA data and is listed as such as a weather service provider on NOAA's site[2]. Although they ostensibly augment it with other sources and apply their own forecasting models to the data, they're still basically repackaging NOAA data in one form or another.
[1] https://en.wikiquote.org/wiki/Turtles_all_the_way_down
[2] https://www.ncdc.noaa.gov/success/weather-service-providers
... in the USA. But one of its great advantages is the data it receives from tens of thousands of amateur weather reporting stations globally. The Wunderground forecast for our locality is hyper-localised and very accurate for that reason, particularly compared to the national Met Office forecast which applies to an airport 35 miles away, beside a lake and on the other side of mountains.
I remember fondly using their Wunder Radio app in the early iPhone years.