Yahoo API is not supported anymore you can try ClimaCell API which is free for a developer account. I have been using this for my many projects or you can write a wrapper around this API to suit your needs.
https://www.climacell.co/weather-api/
They have pretty detailed documentation with sandbox testing if you would like. I found their forecast is very accurate and it goes back by 20 years if you want to work with big data or analyze historical climate change.
Try their real time api
https://developer.climacell.co/v3/reference#get-realtime
Also you can setup webhooks to recieve notifications and postbacks for weather updates or your users can setup alerts for weather changes of any specific locations.
I have multiple mobile apps on which I use their API and its the best one I have came across yet. Thought of sharing it with you.