WhetherReport

Between 25 Dec 2020 – 28 Jan 2023, Meteorological Service Singapore (MSS) made a total of 1,040,721 2-hour weather forecasts. 116,221 of them turned out to be incorrect, resulting in an overall accuracy rate of 88.83%.

The 2-hour forecasts were most accurate in relation to Jurong East (90.81%) and least accurate in relation to Lim Chu Kang (87.29%).

It seems that MSS may have 'wet bias', i.e. a bias towards predicting rainy weather.

It appears that MSS tends to predict rainy weather significantly more often than rainy weather actually occurs — it rained about 4.92% of the time in any given region, whereas 17.32% of MSS's forecasts predicted rainy weather.

This has affected the accuracy of MSS's predictions. Its predictions that the weather would be non-rainy are accurate 94.95% of the time. However, where MSS predicted there would be rainy weather, it only actually rained 59.61% of the time.

This project tracks the accuracy of the 2-hour weather forecasts made by MSS (also available on NEA's myENV mobile app) by comparing rainfall recorded by the National Environment Agency's weather stations against the 2-hour forecasts made by MSS for the same time period. Please note the following:

  • Only MSS's 2-hour weather forecasts are currently being analysed
  • MSS's historical forecast data and NEA's historical weather conditions data are not fully comprehensive, and any missing or invalid data is ignored
  • Since MSS's forecasts do not necessarily cover the same location where NEA's weather stations are located, data from the closest few stations are used. It is therefore possible, e.g. that rainfall predicted by MSS is not recorded by NEA's weather station
  • Weather forecasts are assessed leniently, i.e. if MSS forecasts rain in any form (e.g. Light Showers, Drizzle, Heavy Rain, Thundery Showers, etc.), and there is any precipitation at all within the 2-hour period covered by that forecast, it is considered to be correct (and vice-versa for non-rain forecasts, e.g. Windy, Fair, Cloudy, etc.)

The data used is obtained from data.gov.sg and was made available under the terms of the Singapore Open Data Licence v1.0