Apparently DarkSky does use the NOAA data, whereas Apple was pulling data from The Weather Company, now part of IBM.
"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...
"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...
per https://twitter.com/ajblum/status/1245045062112813059