7 Day Weather Forecast

Why only 7-day weather forecasts?

Some weather sources will publish 10-day forecasts, but we here at wunderground.com only publish up to a 7-day forecast. Why you may ask? Because the quality of weather forecast greatly diminishes after day seven of a forecast. Read below to find out why.

How we get our Forecasts:

The wunderground.com proprietary forecasting model, BestForecast, provides the world's most localized, reliable weather forecasts; ingesting 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.

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 - and with more data points than any other weather source we are better positioned to do this.

How we get our 7-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 7-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 even tell you how accurate our forecasts are:

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