Flood Hazards
This type of flooding occurs when rivers or streams exceed their banks, usually due to prolonged or intense rainfall, but also from dam failures, rapid snowmelt, and ice jams.
River Flooding
This type of terrain produces rapid runoff and quick stream response since the water will travel downhill at greater speeds into rivers and over land.
Mountains or Hills
River Flooding is categorized by the National Weather Service as Minor, Moderate, and this upper category that oftentimes leads to extensive inundation of structures, and sometimes even significant evacuations.
Major
In March of 2024, the National Weather Service unveiled this new display of water resources information, combining the functionality of the legacy Advanced Hydrologic Prediction Service (or AHPS) with new tools from the National Water Center to help partners and the American public make critical water decisions.
National Water Prediction Service
Over half of all flood-related drownings occur due to this activity around hazardous flood water. Turn around, don’t drown!
Driving
This type of flooding is characterized by a rapid and extreme flow of high water into a normally dry area, generally within six hours of the causative event (e.g., intense rainfall, dam failure, ice jam).
Flash Flooding
This is a measurement of the water content obtained if all snowpack at a location melted instantly.
Snow Water Equivalent
A structure installed beside a stream or river that contains equipment that measures and records the stage of the stream.
Steam gauge or Gauge
This model was operationalized in 2016, and simulates observed and forecast streamflow for over 2.7 million stream reaches over the entire continental United States (CONUS), southern, Hawaii, Puerto Rico and the US Virgin Islands.
National Water Model
This federal program helps communities create plans for reducing the impacts of floods and strengthening flood resilience.
National Flood Insurance Program (NFIP)
Changes were made to NWS hydrology products in 2021 as part of the NWS Hazard Simplification Project. The Flash Flood Watch and Flood Watch is now consolidated to Flood Watch when the immediate cause is this.
Heavy Rainfall or Excessive Rainfall
In areas where wildfires have occurred, vegetation has been burned away and soil properties may have been altered, leaving behind these areas of bare ground that tend to repel water, often leading to flooding that can produce mud and debris flows.
Burn scars
These National Weather Service offices provide hydrologic guidance in collaboration with agencies like the US Geological Survey, US Bureau of Reclamation, US Army Corps of Engineers, and many state and local emergency managers across the country.
River Forecast Centers
This experimental product features a seven-day infographic and key messages with an assessment of flood risk, leveraging various sources of NWS water resources forecast information.
Flood Hazard Outlook
To help minimize the risk of flooding in a community, this type of structure is built to redirect floodwaters away from buildings and infrastructure.
Levees or Flood Barriers
This type of warning is issued when a severe threat to human life and catastrophic damage from a flash flood is happening or is imminent.
Flash Flood Emergency
FEMA defines this as the inundation of property in the built environment, particularly in more densely populated areas, caused by rain falling on increased amounts of impervious surfaces and overwhelming the capacity of drainage systems.
Urban Flooding
The Southeast River Forecast Center routinely uses this many hours of forecast rainfall into their river forecasts.
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These static Flood Inundation Mapping libraries are available at select sites across the country and provide inundation extents derived from official NWS flood categories (Action, Minor, Moderate, Major, and Record where available).
Categorical Flood Inundation Mapping (CatFIM)
Starting in 2020, only flash flood warnings with a damage threat tag of either “considerable” or this damage threat will trigger a Wireless Emergency Alert (WEA).
Catastrophic
These are characterized by the sudden, rapid, and uncontrolled release of impounded water or the likelihood of such an uncontrolled release.
Dam Failure or Dam Breach
Many of the record flood events along major rivers in Alaska are the result of these, which are common during the winter and spring along rivers and streams in the higher latitudes.
Ice Jams
This is also known as the river’s water level, as read by a stream gauge or tide gauge.
Stage
NWS Flood Inundation Mapping services depict inundation extent where the National Water Model is signaling this base-level threshold that aligns with the “Action” flood category within each region.
High water
This National Weather Service entity issues your local watches and warnings, including flood and flash flood watches and warnings for your area.
Weather Forecast Office or Local Forecast Office (or WFO)