These are the course materials for UD811.
Unfortunately the Firebase Open Data Set APIs have recently been shut down. They still return data from March 31st, but are no longer updating.
For live data, with lots more cities, try Forecast.io. You'll need to register for an API key, and set up a proxy as it does not allow CORS requests.
There's an included proxy (forecast-io_proxy.js) that will work for local development, but won't work when published live.
Proxies to check out: