History of Severe thunderstorm warning in Timeline

A severe thunderstorm warning is issued by weather agencies when severe thunderstorms are imminent or occurring, posing a direct threat to areas in their path, typically within an hour. These storms can bring large hail, high winds, and torrential rainfall, leading to property damage and injuries. Warnings are based on Doppler radar detection, spotter observations, or reports from emergency services or the public. The specific criteria for issuing a warning vary by country, but the purpose remains the same: to alert people to immediate danger from severe weather.

October 2007: NWS issues warnings on a per-county basis

Prior to October 2007, the National Weather Service issued severe thunderstorm warnings on a per-county basis.

January 2010: NWS upgrades hail size criterion for severe thunderstorm warnings

In January 2010, the National Weather Service upgraded the hail size criterion for a thunderstorm to be considered severe from 0.75 inches to 1 inch in diameter. This change was made due to public complacency from frequent warnings and studies showing hail needed to be one inch to cause significant damage.

March 2012: NWS implements Impact Based Warning system

In March 2012, the National Weather Service implemented a multi-tier Impact Based Warning (IBW) system. Severe thunderstorm warnings and Severe Weather Statements then included event tags with estimates of wind speeds and hail size, and a summary of impacts to life and property.

March 2013: Expansion of Impact Based Warning system

In March 2013, the categorical threat and damage indicator text of the Impact Based Warning system expanded to 33 additional Central Region Weather Forecast Offices after initially being implemented at six NWS offices in Kansas and Missouri.

2013: Implementation of Impact Based Warning system for tornado warnings

Since the 2013 implementation of its Impact Based Warning system for tornado warnings, categorical criteria was introduced to further explain to the public the dangers of some thunderstorms, especially those that occur in the Great Plains.

March 2014: Further Expansion of Impact Based Warning system

In March 2014, eight additional Weather Forecast Offices operating within the Eastern, Southern and Western Region divisions began using the Impact Based Warning indicators, further expanding the system's reach.

2016: Nationwide Implementation of Impact Based Warning system

In 2016, the Impact Based Warning system was fully implemented across the entire National Weather Service, standardizing the format nationwide.

August 16, 2019: NWS incorporates 'emergency' wording into a Severe Thunderstorm Warning

On August 16, 2019, the National Weather Service in Cheyenne, Wyoming incorporated the 'emergency' wording into a Severe Thunderstorm Warning to denote that three-inch diameter hail was imminent in portions of Scotts Bluff, Banner and Sioux Counties in Nebraska.

July 28, 2021: NWS incorporates damage threat indicators for severe thunderstorm warnings

Since July 28, 2021, the NWS has incorporated categorical damage threat indicators for higher-end hail and/or wind events at the bottom of text products for severe thunderstorm warnings, including update statements to existing warnings issued as Severe Weather Statements.