Graph 1: Percentage of High Temperature Forecasts within Three Degrees
Graph 2: High Temperature Forecast Root-Mean-Squared Error.Graph 2: High Temperature Forecast Root-Mean-Squared Error.

The study is the largest and most comprehensive study of its kind done to date with over 55,000 individual weather forecasts compared over a six-month period. High temperatures were compared since they were determined to be the most accurate gauge for forecast comparison. The study was performed over a six-month period from January to June 2003 and compared the forecasted high temperatures for the 20 largest metropolitan areas in the United States to the actual temperature readings as reported by the National Weather Service for those locations. Forecast verification was done on a daily basis and compared the forecast in the evening with the actual result the next day. The other weather providers included in the study were Accuweather, Intellicast, and Weather.com. Unisys and WeatherForYou were also included, as they derive their forecasts from the National Weather Service zone forecasts. In all categories of the study, CustomWeather's website received the number one ranking for forecast accuracy.