Floods

How NWS River Forecasts Work, and Where to Find Them

By the Water Level Atlas team · Last reviewed Oct 21, 2026

Official US river forecasts come from the National Weather Service (NWS), part of NOAA. Thirteen regional River Forecast Centers run computer models that combine observed and forecast rain and snow with river gauge data to predict how high rivers will rise at set locations called forecast points. The forecasts are published at water.noaa.gov, and local NWS offices use them to issue flood watches and warnings.

Who makes river forecasts?

NOAA has 13 River Forecast Centers (RFCs). Each one covers a large region, for example the Ohio, Missouri Basin, Northwest and West Gulf RFCs.

Each RFC serves a group of local NWS Weather Forecast Offices. The RFC produces the river forecast; the local office uses it, along with other information, to decide whether to issue flood watches and warnings for its area.

How is a river forecast made?

An RFC forecast is built in steps:

1. Measure what has already fallen. Forecasters combine rain gauge networks (official and volunteer) with radar estimates of rainfall. Snow on the ground is tracked too, because it stores water that can run off later.
2. Add forecast rain and snow. Forecasters add predicted precipitation for the coming hours or days. How much future rain goes into the forecast varies. The North Central RFC, for example, uses 1 day of future precipitation in the warm season (April to September) and 2 days in the cool season (October to March).
3. Model the runoff. Rainfall-runoff models estimate how much water soaks into the soil and how much runs off, based on soil moisture and the shape, slope and land cover of each basin. Snowmelt is calculated from air temperature and sunshine.
4. Route the water downstream. The models move the water down the river network to each forecast point, adding flow from upstream.
5. Include dam releases. Planned releases from reservoirs run by the US Army Corps of Engineers, the Bureau of Reclamation and others are built into downstream forecasts.
6. Convert flow to height. The forecast flow is turned into a water height (stage) using the rating curve for that gauge. See gauge height vs streamflow.

Forecasters then check the result against recent river behavior and adjust it using their experience.

What is a forecast point?

A forecast point is a place, typically a river gauge, where the NWS issues an official river forecast. According to NOAA's 2024 announcement of its new water website, NWS river forecasts cover about 4,000 locations. Many smaller streams and gauges have no official forecast.

At forecast points, the NWS also sets flood categories (action, minor, moderate, major) in gauge height, so a forecast crest can be read against them. See flood stages explained.

How often are forecasts issued?

It varies by RFC, season and river conditions. As one example, the California-Nevada RFC says it issues routine forecasts at least once a day all year and at least twice a day during its winter flood season, and more often when current or expected river levels pass set criteria. NOAA says its river flood forecasts look up to 7 days ahead. Always check the issue time on the official forecast.

How accurate are river forecasts?

They are the best official guidance available, but they carry uncertainty. The NWS explains that:

• forecasts become less certain the further ahead they look;
• errors in forecast rainfall, both how much falls and exactly where, carry through into the river forecast;
• small basins are harder, because a small shift in where rain falls can put it in a different basin entirely, while large basins can absorb some error.

Because of this, forecasts can change from one issue to the next. NOAA's water site also offers ensemble forecasts (the Hydrologic Ensemble Forecast Service), which show a range of possible outcomes rather than a single line.

Where can I find official forecasts?

The official source is NOAA's National Water Prediction Service at water.noaa.gov. It became fully operational on March 27, 2024, replacing the older AHPS river pages. Each forecast point has a hydrograph showing recent observations and the forecast together, plus flood categories and current watches and warnings.

The National Water Model on the same site gives automated guidance for millions of river reaches without gauges. That guidance is not the same as an official RFC forecast at a forecast point. For warnings, follow your local NWS office and local authorities.

Using this on Water Level Atlas

Where a USGS gauge matches an NWS forecast point, our river page shows NOAA's official forecast as a dashed line on the gauge height chart, the highest forecast level, NOAA flood stages and historic crests, with a link to the official water.noaa.gov page. We never make our own forecasts or warnings. If no forecast point is linked, the page says so and points to water.noaa.gov; see our methodology page.