Here is the summary data
Here is a chart of the data for people who prefer visual:
Points to note
- Openweathermap seems to be the most accurate by far.
- Yr.no has similar accuracy openweathermap for one day in advance, but when predicting further into the future both darksky and yr.no are similar.
- The error from openweathermap seems to be much larger than other services. I checked and this error is genuine.
Like the last time, this analysis lumps all cities together for an average result. I might do some analysis later on performance per city.