National Weather Service Rolling Out New Flood Warning Maps

The National Weather Service (NWS) has launched a nationwide rollout of “experimental” flood forecasting maps. The maps show when, where and how much floodwaters will impact specific areas up to five days in advance.

NWS’s new experimental flood inundation maps help communicate the timing and magnitude of high water events by showing modeled inundated areas in blue overlay. Emergency managers may use these services to preposition resources, secure critical infrastructure and recommend evacuations and evacuation routes.

System Already Rolled Out to Houston Area

NWS has already rolled out the system for Houston and East Texas with other parts of the county to follow.

The new system should enable emergency managers to see how predicted rainfall could impact structures, communities and people.

Until now, the best NWS could do was issue a flood watch or warning for communities. But the new maps will show how far floodwaters could spread in a community. That will help people better prepare for floods and evacuate from them. For instance, it will reportedly show when roads will be cut off by rising waters.

However, the new maps can’t yet forecast urban flash flooding related to lack of storm sewer capacity.

Near Real-Time View for Emergency Managers

NWS announced the new experimental flood maps on September 26, 2023. “These new services complement and support the issuance of flood watches and warnings by providing near-real-time, high-resolution, street-level visualizations showing where, when, and how much flood waters are forecast.”

The descriptions conjure up images of floodplain maps. But they show expected flooding from approaching storms – not just the extent of flooding in a hypothetical 100-year event.

David Vallee, director, Service Innovation and Partnership Division, NOAA’s National Water Center said, “These services will dramatically improve our ability to provide impact-based decision support services to our partners so they can preposition people and resources ahead of flood events.”

Three New Tools

Three new near-real-time services will help improve flood impact information. They include:

Hourly Analysis will model flood inundation extent based on streamflow analysis.
5-Day Maximum Flood Inundation Forecast will model the maximum inundation extent over the next five days for different reaches of a river.
5-Day Max Flood-Inundation River Forecast based on the streamflow predictions when they reach or exceed the action stage.

For more on how the system will work, see this story map based on Houston and Hurricane Harvey. Imagine how many lives could have been saved if we had this system then!

Posted by Bob Rehak on 10/16/23 based on information from NWS

2239 Days since Hurricane Harvey