History of Severe thunderstorm warning in Timeline

A severe thunderstorm warning is issued by weather agencies when severe thunderstorms are imminent or occurring, posing immediate threats like large hail, high winds, and flooding. Unlike a watch, a warning indicates imminent impact within approximately one hour, based on radar detection, spotter reports, or reports from authorities or the public. The criteria for issuing a warning differ across countries, but it universally signifies a heightened risk of property damage and personal injury due to the storm's intensity.

October 2007: Change to Per-County Warning Basis

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

January 2010: Hail Size Criteria Upgrade

In January 2010, the National Weather Service upgraded the hail size criteria for a severe thunderstorm from 0.75 inches to 1 inch. This change was due to public complacency from frequent warnings and studies indicating significant damage only occurred with hail of one inch or larger.

March 2012: Implementation of Impact Based Warning System

In March 2012, the National Weather Service began implementing a multi-tier Impact Based Warning (IBW) system. This system provided estimates of wind speeds, hail size, and potential tornadic development, along with summaries of impacts to life and property.

March 2013: IBW Expansion to Additional WFOs

In March 2013, the Impact Based Warning (IBW) system, initially implemented at six NWS offices, expanded to 33 additional Weather Forecast Offices (WFOs) primarily within the agency's Central Region.

2013: Introduction of Categorical Criteria for Tornado Warnings

In 2013, categorical criteria was introduced to explain the dangers of some thunderstorms, especially those that occur in the Great Plains, that can produce massive hailstones or winds that can cause damage equivalent to hurricanes and tornadoes.

March 2014: IBW Expansion to Additional WFOs

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

2016: Agency-Wide Implementation of IBW Format

In 2016, the entire National Weather Service agency began using the Impact Based Warning (IBW) format.

August 16, 2019: Incorporation of "Emergency" Wording in Severe Thunderstorm Warning

On August 16, 2019, the National Weather Service in Cheyenne, Wyoming, incorporated the "emergency" wording into a Severe Thunderstorm Warning due to the imminent threat of three-inch diameter hail in specific areas of Nebraska.

July 28, 2021: Incorporation of Categorical Damage Threat Indicators

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, and as late as August 2 in certain County Warning Areas.