NOAA’s flood forecasts now reach nearly every American and 3.3 million miles of river

NOAA says the National Weather Service’s Flood Inundation Mapping service now covers nearly 100 percent of the U.S. population and 3.3 million miles of river, up from about 60 percent of residents as of 2025. The service draws a map of where river floodwater could spread, at neighborhood scale, from forecast river flows and current conditions. NOAA still labels it experimental.

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The change is a capability story more than a weather story. Flood warnings have long been tied to a gauge reading at a point on a river. Inundation mapping turns the same forecasts into an area, the streets, buildings and roads that water could reach, and the expansion means that picture now exists for almost every community in the country rather than for a fraction of them.

Flood Inundation Mapping on the National Water Prediction Service

The NOAA announcement, dated September 24, 2026, traces the growth: the service launched in 2023 covering about 10 percent of the population, reached 60 percent in 2025 and now covers nearly all of it across 3.3 million river miles in the continental United States, the territories and Hawaii. The newly added regions are the southeastern coast and Florida, the Great Lakes region, New England, the Rocky Mountains, the Dakotas and western Nebraska.

The maps come from the National Water Model, the national streamflow model, and from the National Weather Service’s River Forecast Centers, and they are published on the National Water Prediction Service website and in several GIS applications and file formats. In the Lower 48 and parts of south-central Alaska the products are an hourly analysis of current conditions plus five-day inundation forecasts from both the model and the River Forecast Centers. Hawaii, Puerto Rico and the U.S. Virgin Islands get the hourly analysis and a 48-hour model forecast.

NOAA’s factsheet for the Lower 48 services gives the cadence: the latest-analysis map updates hourly with about 45 minutes of latency, the River Forecast Center map updates hourly when new forecasts arrive, and the model-driven five-day map refreshes every six hours.

What 3.3 million river miles does and does not mean

The big number covers the whole mapped river network, and the mapping is not equally forecaster-reviewed everywhere. According to the same factsheet, the map built from official River Forecast Center flows exists only downstream of the agency’s forecast points, covering about 110,000 river miles below roughly 3,600 of them. The two model-driven products cover the full Lower 48 domain, and one carries a plain quality-control caveat: a forecaster is not involved in the decision-making process behind it.

The latest-analysis map carries its own limits. The factsheet says it “is not a forecast service” and is limited by the precision of its observed source data, and it is more reliable near river gauges than far from them. All three services share the same terrain grid, so any flaw in the underlying elevation data shows up identically in each.

Alaska’s coverage is narrower. The Alaska services factsheet limits the maps to south-central Alaska, including the Cook Inlet, Kenai Peninsula, Copper River and Prince William Sound watersheds, and it recommends using the River Forecast Center map where available. NOAA lists northern and western Alaska, Guam, the Northern Mariana Islands and American Samoa as still outside coverage.

How forecasters and emergency managers use the maps

NOAA says the Weather Service now uses the maps to communicate maximum river flood potential to emergency managers, medical facilities and other decision-makers. Its release cites cases from the past two years: the Nashville office helped a senior living facility in Macon County evacuate in spring 2025, hours before floodwaters arrived, and the Little Rock office shared the maps with the city of Hardy in April 2025, which evacuated residents door to door.

The release adds Georgetown, Texas, where the Austin/San Antonio office gave the maps to emergency managers during the July 4-7, 2025 storms, informing road closures and evacuations. It also lists the Glover River in Oklahoma in January 2025 and the Muskegon River in Michigan in April 2026. National Weather Service Director Ken Graham said the maps have been “a game changer when briefing emergency managers, first responders, and communities facing flood risk,” and NOAA Administrator Neil Jacobs called inundation maps “a critical tool for assessing the impacts of flooding.”

A companion product covers a different job. Categorical flood inundation mapping is static: it shows flood extent at each official flood category at a gauge, from action stage to record, in one-foot steps up to five feet above major stage. Because it does not depend on streamflow forecasts, it often will not line up with the real-time maps. Residents can find the live maps on the National Water Prediction Service flood inundation mapping page, which carried NOAA’s September 24 notice that the services now cover nearly all of the country.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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