FAQ - Sources

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Forecasts

All of our forecasts are generated from our proprietary forecasting system that leverages our vast collection of neighborhood weather data that we get from our community - we refer to the system as Best Forecast™.

Our ever-expanding network of 22,000+ personal weather stations is the largest of its kind and provides us with a unique ability to provide the most local forecasts based on actual weather data points. BestForecast™ uses the most innovative forecast models available and cross-verifies their output with all of the localized data points. Only our unrivaled amount of local neighborhood weather data can generate forecasts for your front door.

For US locations we give users the option to switch to view the forecasts generated from the National Weather Service’s National Digital Forecast Database (NDFD). In a step to create an unprecedented level of transparency to our forecasting, we publish the recent accuracy of our forecasts for every US location alongside the accuracy of the NDFD forecasts.

U.S. Current Conditions

U.S. current conditions data comes from over 42,000 weather stations across the country including:

  • Almost 2,000 Automated Surface Observation System (ASOS) stations located at airports throughout the country. These are maintained by the Federal Aviation Administration and observations are updated hourly, or more frequently when adverse weather affecting aviation occurs (low visibility, precipitation, etc).
  • Over 16,000 Personal Weather Stations (PWS's) that are part of Weather Underground's ever-expanding PWS network. Stations are put through strict quality controls and observations are updated as often as every 2.5 seconds.
  • Over 26,000 weather stations that are part of the Meteorological Assimilation Data Ingest System (MADIS) which is managed by the National Oceanic and Atmospheric Administration (NOAA). For further information, see http://www-sdd.fsl.noaa.gov/MADIS.

When a visitor requests current conditions from wunderground.com, the geographically closest station is displayed. There is also a "Station Select" button, which shows a list of the next closest stations.

International Current Conditions

International current conditions are collected directly from more than 29,000 weather stations located in countries around the globe including:

  • About 6,000 automated weather stations operating at airports. Here is a list of the stations. Typically these stations are owned by government agencies and international airports and data is updated at 1, 3, or 6 hour intervals, depending upon the station.
  • Over 8,000 Personal Weather Stations (PWS's) and 16,000 MADIS stations.
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