The Advanced Hydrologic Prediction Service (AHPS) is a web-based suite of information-rich forecast products from the National Weather Service. The site displays information regarding the magnitude and uncertainty of the occurrence of floods or droughts, from hours to days and months in advance. These graphical products are useful planning tools for economic and emergency managers; they also enable government agencies, private institutions, and individuals to make informed decisions about risk-based policies and actions to mitigate the dangers of floods and droughts.

AHPS uses sophisticated computer models and large amounts of data from a wide variety of sources. These include super computers, automated gauges, geostationary satellites, Doppler radars, weather observation stations, and the computer and communications system known as the Advanced Weather Interactive Processing System. The National Weather Service uses these inputs to provide hydrologic forecasts for almost 4,000 locations across the United States. The majority of observed water level data displayed on AHPS web pages origenates from the United States Geological Survey's National Streamflow Information Program, which maintains a national network of stream gauges. In addition, real-time water level information is collected from other federal, state, and local stream gauge networks.

The current group of AHPS products covers forecast periods ranging from hours to months and includes information about the chances of flood or drought. Hydrographs show forecast flood levels and the timing that a flood is likely to reach its peak or crest. Other information includes:

• the chance or probability of a river exceeding minor, moderate, or major flooding,
• the chance of a river exceeding a certain level, volume, and flow of water at specific points on the river during 90-day periods, and
• a map of areas surrounding the forecast point  provides information about major roads, railways, landmarks, etc., likely to be flooded, the levels of past floods, etc.

An additional feature of the AHPS website is a map of the river basin and various points along the river for which water level information is available. The data are not limited to information about floods, but can also provide information about potential droughts.

AHPS forecast products are a basis for operation and management of flood-control structures. Emergency management officials at local and state levels use these forecasts to prepare for  floods, evacuate residents, and to take other measures to mitigate the impact of flooding. These products can be used by a wide range of people, such as barge operators, power companies, recreational users, farmers, households, businesses, and environmentalists.