Miller and Fawbush soon would distribute their tornado forecasts to the American Red Cross and Oklahoma Highway Patrol, after giving William Maughan, chief meteorologist at the U.S. Weather Bureau's Oklahoma City office (who provided them with additional archived weather data to help fine-tune their forecasts), permission to relay their forecasts to those agencies. The relative accuracy of the forecasts restarted a debate over their reliability and whether military or civilian agencies should have jurisdiction over the issuance of weather warnings. The USAF had pioneered tornado forecasting and tornado warnings, although John P. Finley had developed the first experimental tornado forecasts in 1885. Two years later, he and other officials with the agency were prohibited by the United States Signal Service's weather service from using the word "tornado" in forecasts. They were instead directed to refer to "severe local storms". This position on tornado forecasting would be shared by the U.S. Weather Bureau after its formation in 1890, fearing that tornado forecasts were insufficiently reliable and that such warnings would incite panic among the public. The side effect of this policy was that the lack of warning resulted in a steady increase in the number of tornado-related fatalities through the 1950s, with some events prior to 1948 (such as the deadliest tornado in U.S. history, the Tri-State Tornado in March 1925, and the Glazier–Higgins–Woodward tornadoes in April 1947) having death tolls well over 100.
Advances in technology, both in identifying conditions and in distributing warnings effectively, have been credited with reducing the death toll from tornadoes. The average warning times have increased substantially from -10 to -15 minutes in 1974 to about 15 minutes As of 2013 (in some cases, the lead time can extend to more than an hour's warning of impending tornadoes). In the United States, the tornado death rate has declined from 1.8 deaths per million people per year in 1925 to only 0.11 per million in 2000. Much of this change is credited to improvements in the tornado warning system, via the various advances in the detection of severe local storms, along with an increase in reports visually confirming severe weather activity via storm spotters, public officials and citizens.
In 1938, the Weather Bureau rescinded its ban on the usage of the word "tornado" in weather products disseminated to emergency management personnel. The Bureau would develop a network of volunteer storm spotters in the early 1940s during World War II, to provide warning of tornadoes to workers in munitions plants and strategic factories. The ban on issuing tornado warnings to the general public would not be revoked until Chief of Bureau Francis W. Reichelderfer officially lifted the ban in a Circular Letter issued on July 12, 1950, to all first order stations: "Weather Bureau employees should avoid statements that can be interpreted as a negation of the Bureau's willingness or ability to make tornado forecasts", and that a "good probability of verification" exist when issuing such forecasts due to the difficulty in accurately predicting tornadic activity. The American Meteorological Society agreed to have Miller and Fawbush present their methodology for forecasting tornadoes during the organization's 1950 meeting in St. Louis; after garnering press coverage for their successful prediction of past tornadoes, AMS representatives decided to open the presentation to the public.
The first official tornado forecast—and tornado warning—was made by United States Air Force Capt. (later Col.) Robert C. Miller and Major Ernest Fawbush, on March 25, 1948. The first such forecast came after the events that occurred five days earlier on March 20, 1948; Miller – a California native who became stationed at Tinker Air Force Base three weeks earlier – was assigned to work the late shift as a forecaster for the base's Air Weather Service office that evening, analyzing U.S. Weather Bureau surface maps and upper-air charts that failed to note atmospheric instability and moisture content present over Oklahoma that would be suitable for producing thunderstorm activity, erroneously forecasting dry conditions for that night. Thunderstorms soon developed southwest of Oklahoma City, and at 9:30 p.m., forecasters from Will Rogers Airport sent a warning to Tinker that the storm encroaching the city was producing wind gusts of 92 miles per hour (148 km/h) and a "Tornado South on Ground Moving NE!" Base personnel received an alert written by the staff sergeant on duty with Miller, minutes before the twister struck Tinker several minutes later around 10:00 p.m., damaging several military aircraft (with total damage estimated at $10 million) that could not be secured in time before it crossed the base grounds.
Borum, who had put together a severe weather safety plan for base personnel, then suggested that Miller and Fawbush issue a severe thunderstorm forecast, and then asked the men if they would issue a tornado forecast based on the similarities between the conditions that produced the tornado which hit the base five days earlier, which they were reluctant to do. Fawbush wrote the forecast message that Miller would type and issued it to base operations at 2:50 p.m. as thunderstorms were approaching from North Texas. Defying the high odds against two tornadoes hitting the same area in five days, one hit the Tinker campus around 6:00 p.m., to the surprise of Miller (who left the base an hour earlier, believing their forecast would not pan out), who found out about the storm (produced by two thunderstorms that merged to the southwest of Tinker) via a radio report. Miller and Fawbush would not put out another tornado forecast until March 25, 1949, when they successfully predicted tornadic activity would occur in southeastern Oklahoma.
The Air Force began issuing severe weather forecasts relayed to Weather Bureau offices and emergency personnel in tornado-prone regions through the formation of the Severe Weather Warning Center in 1951, before the Bureau's contention that the USAF intruded on its responsibility to relay such forecasts led to the SWWC limiting the release of its tornado forecasts to military personnel; however, the move to prohibit the USAF from widespread releasing of tornado forecasts led to disapproval and heavy criticism from Oklahoma media outlets, given the agency's continued refusal to provide public tornado warnings. The Weather Bureau issued its first experimental public tornado forecast in March 1952, which proved inaccurate and was released too late to become widely available for public consumption; however, a forecast issued the following evening managed to predict an outbreak of tornadoes across most of the warned seven-state area (from Texas to Indiana).
The National Weather Service has the option of issuing a tornado emergency, a severe weather statement with unofficial, enhanced wording that is disseminated when a large, extremely violent tornado is about to impact a densely populated area. This category of weather statement is the highest and most urgent level relating to tornadoes, albeit an unofficial alert product. The first tornado emergency was declared on May 3, 1999, when an F5 tornado struck southern portions of the Oklahoma City metropolitan area, causing major damage exceeding $1 billion. In some cases, such as an F3 tornado that struck the Indianapolis, Indiana metropolitan area on September 20, 2002, a tornado emergency has been declared within the initial issuance of the tornado warning. Not all confirmed tornadoes will be considered a "tornado emergency", and such statements are commonly declared when it is believed that the tornado is at a severity in which it would cause a significant threat to life and property.
Local NWS forecast offices utilize WarnGen software integrated into the Advance Weather Interactive Processing System (AWIPS) to generate the warning statement, which is disseminated through various communication routes accessed by the media and various agencies, on the internet, to NOAA satellites, and over NOAA Weather Radio; additionally, the National Weather Service has the option of requesting activation of the Emergency Alert System (EAS) to interrupt television and radio broadcasts to get the bulletin out quickly. Warnings for tornadoes and severe thunderstorms are outlined in polygonal shapes for map-based weather hazard products distributed to the main agency, individual forecast office websites and the Storm Prediction Center (including open-source APIs available for free use to public weather websites and mobile apps), based on the storm's projected path as determined by Doppler radar at the time of the warning's issuance. In NWS text products, warnings are usually illustrated by individual counties, parishes or other county-equivalent jurisdictions (sections or the entirety thereof, and in list format if it covers more than one jurisdiction), particularly dependent on the jurisdiction's total land area. Prior to October 2007, warnings were issued by the National Weather Service on a per-county basis. SPC and NWS products as well as severe weather alert displays used by some television stations, and desktop and mobile radar software typically highlight tornado warnings with a red or purple polygon or filled county/parish/equivalent jurisdiction outline. (Since the late 2010s, Baron Services broadcast radar software and some public commercial radar software, such as GRLevelX, have used custom polygon coloring to denote tornado warnings based on impact level: usually, purple to indicate warnings for a confirmed tornado and inlined black-on-purple to indicate tornado emergencies.)
Warnings are disseminated to the public through broadcast and online media outlets, and Weatheradio Canada; depending on storm severity and regional office discretion, the warning may require activation of depending on storm severity and regional office discretion, the warning may require activation of the National Public Alerting System (Alert Ready) (French: Système national d'alertes à la population [En Alerte]) and feeding provincial alerting systems (such as Alberta Emergency Alert and SaskAlert) to distribute the alert to local broadcast media and cellular phones. Separately, Emergency Management Ontario—upon implementing the system in 2008—issues red alerts for sections of the province under an Environment Canada-issued tornado warning, and can sometimes override the tornado warning if local government or media outlets participate in the program.
In March 2012, as part of its implementation of a multi-tier Impact Based Warning (IBW) system to notify the public and emergency management officials of the severity of specific severe weather phenomena, the NWS Weather Forecast Offices in Wichita and Topeka, Kansas, and Springfield, St. Louis and Kansas City/Pleasant Hill, Missouri, began incorporating categorical tornado and damage threat indicators for visually confirmed and radar-indicated tornadoes that appear at the bottom of the text products for tornado warnings and associated Severe Weather Statements providing updated storm information. The categorical criteria—which are applicable to all NWS Weather Forecast Offices, primarily those operating within the agency's Central and Southern Region divisions—were introduced to further communicate to the public and prevent complacency of the threat of tornadoes. The NWS expanded the threat and damage indicators to 33 additional Central Region WFOs in March 2013; eight additional offices operating within the Eastern, Southern and Western Region divisions began using the IBW indicators in March 2014. The entire agency began using the format in 2016; IBW formatting was fully implemented for other individual warning bulletins in July 2021, when all NWS offices incorporated damage threat indicators into severe thunderstorm warnings. The threat indicators consist of four coded taglines, ascending by observational level and damage threat:
On August 15, 2020, for the first time in history, the National Weather Service issued a tornado warning for pyrocumulonimbus capable of causing a fire tornado for southeastern Lassen County, California, which was being affected by the Loyalton Fire.
In April 2023, U.S. Sen. Roger Wicker (R–MS) introduced the Tornado Observation Research Notification and Deployment to Operations (TORNADO) Act, The bill would establish a Hazard Risk Communication Office to propose improvements in the National Oceanic and Atmospheric Administration (NOAA)’s methods for predicting severe weather events and communicating weather alerts to the public—requiring NOAA to coordinate with government and emergency management to optimize collection and sharing of storm survey data, implement high-resolution probabilistic tornado forecast guidance systems, and make recommendations for revisions to the Enhanced Fujita Scale.