Web Products
The NWS Advanced Hydrologic Prediction Service (AHPS) monitors more than 3000 river gages across the United States, including American Samoa, Guam, Puerto Rico and the Virgin Islands. Many of these sites are USGS gages that report on intervals of an hour or less. This helps the NWS monitor these gages 24 hours a day, 7 days a week for the threat of flooding. On this page, we’ll discuss NWS Web-based products available from www.weather.gov that provide flood information. Some similar products (also derived from AHPS data) are also available via the HURREVAC model interface discussed in the Emergency Management section.
The "Water" tab on www.weather.gov goes to www.weather.gov/ahps which displays a map (image below) that shows the current flood stage for all of the river gauges in the country. Green data points mean the river is below flood stage, yellow indicates stations near flood stage, and orange, red, and purple squares flag rivers above flood stage. Note that this graphic depicts river flooding, not flash floods.
Example of flood stage map
Clicking on an individual square will bring up a local map (shown below). Squares indicate stations that have only observations, while the diamonds denote stations that also have forecast information.
Example of a local river gauge display
Clicking one of the symbols will display a graph (below) of the past hourly observations (blue line) and the forecast (dotted green line) of the river height at that location for the next several days. The different colors of the background represent various high water levels, with the orange, red, and purple backgrounds highlighting flood stages. In this particular example, recent rains resulted in moderate flooding that was forecast to fall below flood stage on November 24th.
Example of a plot of observations and forecast conditions for a single river gauge
In addition to the river forecasts, you can also look at what impacts may occur as the result of particular river levels. Scrolling down the screen below the river forecast graph, you’ll find a map (below) displaying the location of the river gauge. To the left of the map is a list of record river crests. Below the map is a list of impacts when the river reaches a particular value. This example shows a historic crest of 33.9 ft (10.3 m) occurred on May 20, 1943.
Example of a information about past flood events in the area of this river gauge