History of Severe thunderstorm warning in Timeline

A severe thunderstorm warning is issued by weather agencies when severe thunderstorms are detected or reported, indicating an imminent threat, typically within an hour. These storms pose risks of property damage and injury from large hail, high winds, and flooding caused by heavy rainfall. The specific criteria for issuing a warning differ between countries, but the core purpose remains the same: to alert the public to immediate danger from severe thunderstorms.

October 2007: NWS issued warnings on a per-county basis.

Prior to October 2007, the National Weather Service issued severe thunderstorm warnings on a per-county basis. Local NWS forecast offices outline warnings for tornadoes and severe thunderstorms in polygonal shapes for map-based weather hazard products, based on the storm's projected path as determined by Doppler weather radar at the time of the warning's issuance.

January 2010: NWS updated severe thunderstorm criteria

In January 2010, the National Weather Service updated the criteria for a severe thunderstorm, increasing the hail size threshold from 0.75 inches to one inch in diameter. This change was due to public complacency from frequent warnings and studies showing hail needed to be one inch in diameter to cause significant damage. Severe thunderstorm warnings are issued through local Weather Forecast Offices using WarnGen software within the Advance Weather Interactive Processing System (AWIPS) and disseminated via various communication channels including the internet, NOAA satellites, and NOAA Weather Radio.

March 2012: NWS implemented Impact Based Warning system

In March 2012, the National Weather Service implemented a multi-tier Impact Based Warning (IBW) system. This system included event tags in severe thunderstorm warnings and Severe Weather Statements to summarize straight-line wind speeds, hail size, and potential tornadic development. The product text also provided a summary of impacts to life and property caused by hail and winds.

March 2013: IBW expanded to more NWS offices

In March 2013, the Impact Based Warning (IBW) system, initially implemented in six NWS offices in Kansas and Missouri, expanded to 33 additional Central Region Weather Forecast Offices (WFOs). The categorical threat and damage indicator text was applicable to all Weather Forecast Offices, primarily those operating within the agency's Central and Southern Region divisions.

2013: Categorical criteria introduced to explain dangers of thunderstorms

In 2013, similar to the indicators used for tornado warnings, categorical criteria were introduced to explain to the public the dangers of some thunderstorms. These thunderstorms, especially those in the Great Plains, can produce massive hailstones of baseball size or larger and winds that can cause damage equivalent to hurricanes and tornadoes. When deemed necessary, initial warnings and Severe Weather Statement updates containing the "destructive" tag will be disseminated into the Wireless Emergency Alerts system as well.

March 2014: IBW expanded to additional regions

In March 2014, eight additional National Weather Service offices operating within the Eastern, Southern, and Western Region divisions began using the Impact Based Warning (IBW) indicators.

2016: Entire NWS used IBW format

In 2016, the entire National Weather Service began using the Impact Based Warning (IBW) format for severe thunderstorm warnings.

August 16, 2019: NWS Cheyenne used "emergency" wording in a Severe Thunderstorm Warning

On August 16, 2019, at 1:31 a.m. MDT, the National Weather Service in Cheyenne, Wyoming, incorporated the "emergency" wording into a Severe Thunderstorm Warning. This "severe thunderstorm emergency" statement indicated that three-inch diameter hail, as confirmed by storm spotter reports, was imminent in portions of Scotts Bluff, Banner, and Sioux Counties in Nebraska, specifically around Scottsbluff and Gering.

July 28, 2021: NWS incorporated damage threat indicators

Beginning July 28, 2021 (or as late as August 2 in certain County Warning Areas), the National Weather Service 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 issued as Severe Weather Statements.