Dotted lines :85th (upper) and 15th (lower) percentiles of climatological distribution
The website of Extended Outlook provides the probability forecast of daily minimum and maximum temperatures as well as their trend of variation in the next 14 days. Please click here for the detailed forecast for the 9 days in grey area.
The trend in variation of daily minimum and maximum temperatures are shown in two separate time series that are updated once a day at around noon.
The time series of temperature probability forecasts represent the chance of minimum / maximum temperature to occur within 1 degree of that temperature value. For instance, when the forecast probability of minimum temperature at 28 degrees is 60%, it means that there will be 60% of chance for minimum temperature to occur between 27 and 29 degrees. The gray solid line in the charts denotes the climatological mean, whereas the upper and lower dotted lines denote the 85th and 15th percentiles respectively of the climatological distribution – i.e. there are 70% of the same period in the past with the (minimum or maximum) temperatures falling within the upper and lower dotted lines.
The probability temperature forecasts are automatically generated based on post-processing of outputs from the ensemble forecast system of computer model. The 9-Day Weather Forecast issued by forecasters is based on various meteorological observations, computer forecast model products including the probability temperature forecast and past forecast experience. As the two forecast methods are different, there could be differences between the two forecasts.
According to verification results, the average error of the most probable minimum or maximum temperature forecast compared to the actual recorded minimum or maximum temperature at the Hong Kong Observatory is about 1-2 degrees.