I believe the point of Dark Sky was that they used air-pressure sensor data from the phones they were installed on. That was the secret sauce that (used to) power their hyper-local forecasts.
They claimed something about barometer data but I don't honestly believe that they used it to improve their forecasts. I worked on this problem at different companies for many years, and with academia, and found it to be quite difficult. Possible, doable, but very difficult to demonstrate actual improvement. Significant academic work was done after Dark Sky made their claim, and the papers published used ensemble kalman filters among other on-device data-cleaning techniques that I do not believe Dark Sky implemented. So I doubt their barometer claims.
[1] https://www.zdnet.com/article/dark-sky-weather-app-iphone-6-...