5 Day Weather Forecast

Why 5 day and 7 day weather forecasts, but not 10 day:

The wunderground.com proprietary forecasting model, BestForecast, provides the world's most localized, reliable weather forecasts. The model ingests data from our network of over 20,000 personal weather stations as well as historical data and data from over 12,000 airports around the world. From this data we publish our 5 day weather forecasts.

Weather is not an exact science - to enhance the accuracy of forecasting, we need to understand the existing error base from which to improve. To do this you need to cross verify forecasts with the actual conditions. We here at wunderground.com have more data points than any other weather source and are therefore better positioned to provide reliable and accurate 5 day forecasts.

How we get our 5-day weather forecasts:

For every location in the world, BestForecast analyzes the accuracy of 75 different forecasting models over the previous 2-3 weeks, identifying which model has historically performed the best. BestForecast analyzes every weather variable at every 3-hour time interval going back 14 days. From this data we publish our 5-day forecasts.

The BestForecast model verifies 8 different variables: hourly temp, high temp, low temp, humidity, wind speed, wind direction, cloud cover and pressure.

By multiplying all our data points: 31,000 (stations) x 75 (models) x 112 (time intervals) x 8 (data variables) one gets over 2 billion variables that the model analyzes each time we run the model.

Our 20,000+ personal weather stations essentially fill in the gaps between the airport stations. Most other weather sources have to use data assimilation to fill in these gaps.

We'll tell you how accurate our forecasts are:

The new proprietary forecasting system allows wunderground.com to provide its users with unprecedented levels of transparency by publishing the recent accuracy of its weather forecast 7-days out for each location.