How Does ForecastAdvisor Calculate the Accuracy of Weather Forecasts?

ForecastAdvisor is a service of ForecastWatch. Every day, ForecastWatch collects over 40,000 weather forecasts from over 800 U.S. and Canadian cities from Accuweather, CustomWeather, Intellicast, The National Weather Service, and The Weather Channel. ForecastWatch then takes weather observations from the National Weather Service ASOS (Automated Surface Observing System) network and compares what actually happened with what was forecast.



All the accuracy calculations that appear on ForecastAdvisor are averaged over one to three day out forecasts. The percentages you see for each weather forecaster are calculated by taking the average of four accuracy measurements. These accuracy measurements are the percentage of high temperature forecasts that are within three degrees of what actually happened, the percentage of low temperature forecasts that are within three degrees of actual, the percentage correct of precipitation forecasts (both rain and snow) for the forecast icon, and the percentage correct of precipitation forecasts for the forecast text.

The percentages you see are specifically for the listed city. About 90 forecasts from each provider make up the monthly percent (30 days in a month times 3 days of forecasts per day), and over 1000 forecasts from each provider make up the yearly percent. Take a look at different cities and compare how accuracy differs (Key West, Florida is easier to forecast for than Minot, North Dakota, for example).