NWC REU 2020
May 26 - July 31



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Understanding the Correlation Between NWS Impact-Based Flash Flood Warning Categories and Various NWS Flash Flood Tools

América Gaviria Pabón, Jill Hardy, Jonathan J. Gourley, and Todd Lindley


What is already known:

  • Flash flooding is a dangerous event that causes damage to life and property.
  • The majority of weather-related fatalities are due to flash flood events particularly related to vehicles.
  • Impact Based Warnings allows forecasters to add stronger language to their warning text products.
  • Flash flooding is complicated for forecasters during the warning decision process.

What this study adds:

  • Based on Impact-Based Warning categories (Base, Considerable, Catastrophic), the majority of recent flash flood events from OK and TX are of Considerable impacts.
  • A "roads closed" report is very subjective, and thus, can be classified in either the Base or Considerable categories, which significantly changes the flash flood event IBW distributions.
  • There are common keywords that can be associated with each IBW category which can help forecasters classify flash flood events.
  • Adding a new column of Flash Flood Severity Index to Storm Data Reports will help reduce subjectivity and make it less dependent on forecaster perspective.


Flash floods are dangerous natural hazards that can cause damage to life and property. Currently, they are one of the primary causes of weather-related fatalities in the United States. Recently, the National Weather Service has started issuing an Impact-Based Warnings (IBW) for flash flood events, which allows forecasters to add stronger language to their warning text products based on the impacts that are possible or occurring. The IBW categories are Base, Considerable and Catastrophic. This project classified a database of 141 flash flood events from 2013-2019 bases on their perceived IBW categories using specific keywords found in each report. To help with the classification, information from social media such as Twitter and Facebook posts, news articles, pictures and videos were also analyzed. The classification of the events was done twice depending on how to account for reports of closed roadways. For the first time the results showed that 19.3% of the events were base, 62.1% were considerable and 18.6% were catastrophic. After re-classifying the roadway reports as base (instead of considerable), the results showed that 35.5% were base, 47.5% were considerable and 17.0% were catastrophic. It was concluded that the analysis of the events depends on perspective which creates a major challenge at the time of the classification due to the keywords being ambiguous some of the times.

Full Paper [PDF]