Friday, October 4, 2019

Accuracy of temperature predictions

Using the weather data I collected previously, I wanted to figure out which of the forecasts services was making the most accurate forecasts.

The way I calculated this was by comparing the temperature predicted in x days time with the actual temperature reported by the service. e.g. if the provider predicted on 1st/Aug that the temperature would be x degrees in 5 days time, then I compare this with their actual reported temperature on 6th/Aug, This absolute error is then averaged across all readings from  all cities

Here is the summary data

Here is a chart of the data for people who prefer visual:

Points to note
  • I eliminated one reading from weather underground 6 day forecasts because it would have re-scaled the chart (probably indicates a programming error on my behalf).
  • In general the forecast accuracy decreases as the number of days increases.
  • Yr.no is best for next day, but bluemix and darksky are equally good further out.
  • OpenWeatherMap and Weather underground are significantly worse.

This analysis lumps all cities together for an average result. I might do some analysis later on performance per city.

Weather forecast data


I have published several posts about weather. I also did articles with analysis of temperature and wind forecast, but there is a lot more analysis which could be done. Therefore I decided to publish the raw data in case anyone wants to analyse it. I will also do some more charting/plotting myself.

Click here to download the captured forecasts in CSV format. The file contains over 2 million records in total and the format is fairly self explanatory. It covers a period from June 2017 to December 2018, but some forecasts are missing due to a variety of factors. Most notably the Bluemix data only covers August 2017 to February 2018.

I will later post additional analysis files in this folder with some derived data from this original data in the CSV.

I recently found out about a professional analysis report comparing the accuracy of several forecast providers. I think you should value their results above mine.