River Forecast Centers (2024)

River Forecast Centers (1)

Hydrology is the science of water on Earth – where it occurs and how it circulates through the hydrologic cycle as precipitation, runoff, evaporation, and groundwater.

River Forecast Centers (RFC) are National Weather Service offices that serve groups of Weather Forecast Offices by providing river and flood forecasts and warnings as well as basic hydrologic information. Some responsibilities are seasonal or as-needed, including water supply forecasts, flood outlooks, and drought summaries.

Staff from many different science backgrounds fill RFC forecasting positions of the hydrologic forecaster and hydrometeorological analysis and support (HAS) forecaster. The hydrologic forecast looks at how water and soil interact and how fast the river water flows downstream, called the routing. The hydrologic forecaster is the person who creates the daily river forecasts, flash flood guidance, data summaries, and river forecast computer models. The HAS forecaster prepares the observed and forecast rain/snow and temperature data needed to put into the river forecast model, called the Graphicast. They also support the hydrologic forecaster and the NWS Forecast Offices.

Precipitation Forecasting

Forecasting rivers begins with the rainfall and snowfall forecast. RFC hydrometeorologists and hydrologists prepare precipitation forecasts for multiple days at a time to monitor developing weather systems.

Precipitation Analysis

Multiple organizations and offices maintain gage stations – sites on a river, stream, canal, or other body of water where observations of water level (stage) and flow are measured.

RFC staff hydrometeorologists and hydrologists look at Doppler radar plus rainfall and snowfall measured from the local, state, and federal gage networks to estimate actual rainfall over a region. This information is used in the RFC hydrologic and hydraulic models of how precipitation and runoff flow and how that interacts with the soil and other land features. Observations from the National Weather Service (NWS) Cooperative Observer Program (COOP) observations and the Community Collaborative Rain, Hail, and Snow Network (CoCoRaHS) are also used in this analysis.

This estimated precipitation combined with the forecasted time period allows hydrologists to model how much and when water is expected to reach a river or stream.

River Flow Modeling

To be able to forecast the amount of water flowing through a certain point along a river, the forecaster breaks the flow down into three components:

  • Baseflow: the amount of water coming from groundwater.
  • Runoff: the amount of water flowing over thesurface of the land.
  • Routed Flow: the amount of water coming from an upstream point in the river.


Baseflow, the water coming from groundwater, is never constant. It increases immediately after rainfall, then falls again until the next rainfall.


Runoff comes from two sources, rainfall and snowmelt. A forecaster can estimate the amount of runoff for each location based on certain details about the weather and the land around the river, called the river basin. Snowmelt is calculated based on the air temperature and the amount of sunshine. Rainfall runoff is estimated based on the slope of the land, the amount of paved ground and buildings, the types of soil, the amount of the last rainfall, the time since the last rainfall, and the amount of evaporation occurring over the basin.

When rain begins to fall, the runoff does not immediately go into the river; the amount of time it takes depends on where in the basin the rain fell.

To get a sense of how this works, envision a parking lot with a storm drain at one end. Think of what happens if a steady, even rain falls over the entire parking lot. The rain water doesn't reach the drain all at once because the rain fell at different distances from the drain and needs to travel to it. Even when the rain stops, water will continue to flow into the drain until the water from the farthest part of the parking lot reaches the drain. If the amount of water going through that drain was recorded and put on a graph of water flow versus time, it would look something like this:

River Forecast Centers (2)

Any graph of water flow versus time is called a hydrograph. When a forecast is being made, the forecaster always uses a hydrograph of the stream at the forecast point. From this hydrograph, the forecaster can begin to make a forecast.

A special hydrograph, called the unit hydrograph, is used by forecasters when they want to know how much water will be put into the stream by runoff. The unit hydrograph is based on the basin receiving enough rain to make one inch of runoff. An inch of runoff is the equivalent to having the entire basin of a particular stream or river covered in an inch of rain that does not infiltrate (soak) into the ground. The unit hydrograph shows how much of this inch of runoff will go into the stream in a specific amount of time. For the unit hydrograph to work properly, the length of time in which the runoff was generated and the time intervals on the unit hydrograph must be the same.

A river forecast model adds each of the three flow components mentioned above for every forecast period and converts the total flow to a stage forecast. Six different rainfall-runoff models and three routing methods are widely used by NWS RFCs.

Soil Water Modeling

Several River Forecast Centers use the Sacramento Soil Moisture Accounting (SAC-SMA) rainfall-runoff model. The SAC-SMA is a model that calculates total amount of runoff based on the different types of soils in the area, called soil zones, which absorb water differently. Many different pieces of information are used to show the movement of water into and out of these zones. The model also stores information about the amount of moisture in the soil in order to estimate the amount of runoff when it rains in the future.

A unit hydrograph is used to figure out local water flow based on the runoff calculated from the Sacramento model. The local flow is added to routed flows (the water already in the river) at each gage site to figure out the total flow for each forecast. Total flow is then described as a stage (water level/height) forecast based on the relationship between stage and flow at each specific gage site.

Heavy rainfall will affect any portion of the river, but the most sensitive areas during or immediately following rainfall are the small streams, tributaries, and headwaters that flow into the mainstem rivers. These areas can very quickly have hazardous flash flooding. However, these flows can recede just as quickly as they rose, creating short-term flooding conditions.

Mainstem River Forecasting

River Forecast Centers (3)

Modeling river flow involves many pieces that must work together to create an accurate forecast. One factor, soil moisture, is modeled to estimate how much of the rainfall will actually become runoff rather than remain in the soil. A second factor is lag, the time it takes for the runoff to reach gage A, the first gage in a network. A third factor is attenuation, which is how the wave of water spreads out as it flows downstream. Channel losses – water that infiltrates into the bed of the river – can also be modeled if appropriate for the local hydrology.

Once the lag and attenuation are determined for various flowrates and stages, the water is routed to the next gage (gage B) downstream. This flow then combines with the local runoff between gage A and B to create the forecast for gage B. This process continues all the way downstream (e.g., A to B, B to C, C to D, etc.).

Water released from reservoirs by the Corps of Engineers, the Bureau of Reclamation, river authorities, and water districts are also coordinated and included in all forecasts. Additionally, the U.S. Geological Survey (USGS) and other agencies provide accurate flow and stage observations during flood events for use with the forecasts.

Below is a map of the river forecast centers and their areas of responsibility. Click or select on image below or use the drop down menu to go to any office.

River Forecast Centers (4)

The RFC provides hydrologic guidance for time scales that vary from hours (flash flood guidance and support to Local Flood Warning Systems) to days (traditional flood forecasts) to weeks (snowmelt forecasts), to months (seasonal water supply), as seen in the figure below.

River Forecast Centers (5)

The RFCs are firmly committed to providing the best possible river forecast guidance. Improvements come in the form of expanded coverage and increased quality. Efforts are continuously underway to improve the process used to forecast flooding, spring snowmelt, and water supply volumes.

River Forecast Centers (2024)


How many river forecast centers exist in the United States? ›

Map of the 13 River Forecast Centers and their areas of responsibility.

What are the duties of the river forecast centers? ›

NWS River Forecast Centers have four basic functions: Continuous hydrometeorological data assimilation, river basin modeling, and hydrologic forecast preparation. Technical support and interaction with supported and supporting NWS offices. Technical support and interaction with non-NWS partners and customers.

How high does the river level along this section of Buffalo Bayou need to reach to be considered a flood stage? ›

Traces and Thresholds Click to turn on/off display
Major Flooding60 ft
Moderate Flooding57 ft
Minor Flooding52 ft
Action49 ft

How are river floods predicted? ›

Forecasts typically use storm runoff data, reservoir levels and releases to predict the rise in river levels. In Northern California the National Weather Service, in cooperation with the state's California-Nevada River Forecast Center in Sacramento, forecasts flooding.

Where is the World Area Forecast Center WAFC located in the United States? ›

The U.S. WAFS forecasts are provided by the Washington World Area Forecast Center (WAFC). The Washington WAFC is operated by the United States National Weather Service (NWS).

What is an atmospheric river USA today? ›

What is an atmospheric river? Atmospheric rivers pick up water vapor from the warm, moist air of tropical regions and then drop the water over land in cooler regions as rain or snow.

Who maintains the weather stations that are in the weather underground? ›


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 250,000 Personal Weather Stations (PWS's) that are part of Weather Underground's ever-expanding PWS network.

What are the special NWS forecast centers responsible for? ›

Question: Question 33Special NWS forecast centers have responsibility forissuing hurricane watches and warnings. issuing tornado and severe thunderstorm watches. issuing river, reservoir, and flood forecasts. all of the above are correct.

What does a hydrograph show? ›

A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a river, channel, or conduit carrying flow. The rate of flow is typically expressed in cubic meters or cubic feet per second (cms or cfs).

How big is Buffalo Bayou? ›

Buffalo Bayou
• locationGalveston Bay
• coordinates29.761408°N 95.086903°W
Length53 miles (85 km)
Basin size500 square miles (1,300 km2)
19 more rows

How fast is the Buffalo River? ›

The river moves at an average of 2 mph, allowing canoes to float over most rocks. High: For experienced floaters only. The river flows swiftly and compromising situations may occur.

What is the Mississippi River level at New Orleans? ›

Latest Data 07/08/2024 10:00 Central
Latest Stage4.42 Ft.
24 Hr. Change0.00 Ft.
Tomorrow's Forecast (Issued 07/08/2024 15:54)4.30 Ft.
24 Hr. Precip Total0.00 In.
4 more rows

How to tell if a flood is coming? ›

You may notice a stream starting to rise quickly and become muddy. Sometimes flood debris temporarily blocks the water flow upstream. When it breaks free the debris may release a “wall of water” downstream. You may hear a roaring sound upstream as a flood wave moves rapidly toward you.

Where is a river most likely to flood? ›

Relief - a steep valley is more likely to flood than a flatter valley because the rainfall will run off into the river more quickly.

What is the most common cause of river flooding? ›

Flooding typically occurs when prolonged rain falls over several days, when intense rain falls over a short period of time, or when an ice or debris jam causes a river or stream to overflow onto the surrounding area. Flooding can also result from the failure of a water control structure, such as a levee or dam.

How many National Weather Service locations are there? ›

There are 122 NWS Weather Forecast Offices across the nation serving areas that typically consist of 20 to 50 counties (more info). Each office has its own social media accounts to keep you informed and up-to-date on the latest forecasts, watches and warnings for the local area.

How many states rainfall ends up in the Mississippi river? ›

With its many tributaries, the Mississippi's watershed drains all or parts of 32 U.S. states and two Canadian provinces between the Rocky and Appalachian mountains.

What is the Organic Act of the Weather Service? ›

Then, Congress passed the Organic Act of 1890, that transferred all weather and related river services into the Department of Agriculture, and created a civilian U.S. Weather Bureau, which would later become the National Weather Service (NWS). As the country grew, the need for expanded hydrologic services grew with it.

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