Information About Our Data

U.S. Current Conditions

U.S. current conditions data comes from over 18,000 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 8,500 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 7,500 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, along with a pull-down menu of the three next closest stations.

International Current Conditions

International current conditions are collected directly from more than 8,000 weather stations located in countries around the globe. 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.

Our PWS network also has over 3,000 Personal Weather Stations outside the US that send us current conditions, updated as often as every 2.5 seconds.

U.S. Forecasts

U.S. forecasts and advisories on wunderground.com are generated by the National Weather Service (NWS) that issues forecasts specific for every county in the U.S. two to four times per day, or more often when conditions warrant. Forecasts are also pulled from the National Digital Forecast Database (NDFD) that gives granular forecasts down to the postcode with hourly detail.

International Forecasts

We use a cutting edge proprietary forecasting system that analyses historical weather data and past model performance to achieve the best possible forecasts for locations around the globe. The system is named 'Best Forecast' and we believe that it lives up to its name!

Weather Underground's dedicated team of meteorologists continually strives to further improve the quality of our data and the Weather Underground PWS network is constantly expanding. We are committed to delivering the most reliable and comprehensive weather data available.