Weather affects us every day. It influences our choice of clothing and activities, and even our state of mind. Weather has an enormous impact on the economy, food supplies and transportation. And when it turns nasty, it can bring extreme hardship and destruction.

Making accurate weather forecasts is critical but very difficult. It requires a highly precise and global understanding of the atmosphere, oceans and land. Slight discrepancies in temperatures, humidity or winds in computer models can cause large discrepancies in forecasts.

Hurricane Dora building force in the Pacific Ocean, August 10, 1999.

The National Weather Service, part of the National Oceanic and Atmospheric Administration (NOAA), operates many of the satellites that provide meteorologists with the information and images they need to forecast weather. NASA and JPL also build and fly instruments that accurately observe specific components of weather, such as temperature, clouds and winds. NOAA and other scientists use this data to improve forecasts and learn more about how Earth's weather and climate system works.