A tornado warning is issued when any of the following conditions has occurred: • a tornado is reported on the ground, or • a
funnel cloud has been reported, or •
strong low-level rotation is indicated by
weather radar, Used in tandem with Doppler weather radar information, eyewitness reports can be very helpful for warning the public of an impending tornado, especially when used for ground truthing. 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 (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.
Regional basis United States In the United States, tornado warnings are issued by local
Weather Forecast Offices of the National Weather Service, which, in conjunction with the
Storm Prediction Center, maintains a multi-tier public warning system to disseminate probabilistic outlooks and alerts for tornadoes: •
Convective Outlook (categorical and probabilistic forecasts issued at least twice per day to describe threats of general or severe convective storms; severe thunderstorm outlooks for the Day 1 and Day 2 periods include charts and maps assessing tornado probabilities) •
Public Severe Weather Outlook (issued when a significant or widespread
severe thunderstorm/
tornado outbreak is expected or, particularly from November to March, when strong tornadoes are forecast to occur after nightfall) •
Tornado Watch •
PDS Tornado Watch (upgraded wording indicating the likelihood of a significant tornado outbreak and/or a credible threat of strong to violent tornadoes within the watch area) • Tornado Warning • PDS Tornado Warning •
Tornado Emergency 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: • Radar Indicated – Doppler weather radar indicates the thunderstorm is exhibiting mesocyclonic circulation supportive of tornado formation; generally requires no visual confirmation of a tornado at the time the initial warning or a subsequent severe weather statement is issued. Hazard statements will classify the tornadic rotation as "radar indicated" or "radar-indicated rotation" in the bulletin text when identifying the source of the hazard. • Observed – Tornado is visually confirmed by storm spotters, law enforcement or other emergency personnel, or detected on radar in concert with an observed
intense velocity couplet and/or
debris signature. Hazard statements within the bulletin text will indicate a "damaging tornado." • Considerable (originally "Significant" during the 2012 Kansas and Missouri tests) – Typically reserved for PDS tornado warnings, it indicates credible evidence exists (through visual or radar confirmation) that a tornado capable of producing considerable damage is imminent or ongoing. As with warnings containing the "observed" tag, bulletins with this indicator will classify a "damaging tornado" in the hazard statement. • Catastrophic – Generally reserved for warnings containing Tornado Emergency wording, it indicates reliable sources have confirmed a violent tornado posing a severe threat to human life and catastrophic property damage is occurring. In most instances, bulletins with this indicator will classify a "deadly tornado" in the hazard statement. On August 15, 2020, for the first time in history, the National Weather Service issued a tornado warning for
pyrocumulonimbus capable of producing a tornado in 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.
Canada In
Canada,
Environment and Climate Change Canada issues tornado warnings through regional
Meteorological Service offices based in
Vancouver,
Edmonton,
Winnipeg,
Toronto,
Montreal and
Dartmouth for specified municipalities and
census subdivisions. Although issuance criteria are similar to the U.S. National Weather Service, Meteorological Service-issued tornado warnings can include areas not in the immediate approximate path of the tornadic thunderstorm but are in an environment conducive to tornado development from adjacent thunderstorms during the warning timeframe (similar to but covering a smaller total area than tornado watches issued by the U.S. Storm Prediction Center). 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) () 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. Since implementation of the colour-coded warning system, the Weather impact guides state the following according to Environment Canada's MSC for adverse impacts expected from violently rotating, damaging winds associated with thunderstorms:
Moderate • Travel routes difficult or dangerous to navigate • Travel delays due to road closures, debris, power outages • High-sided vehicles pushed around • Local utility/power interruptions or outages • Outdoor events postponed or cancelled • Damage to trees • Minor damage to property including buildings, vehicles, signs, fences, loose items • Risk of injury from flying or falling debris
High • Travel routes dangerous to navigate • Widespread travel disruption • Widespread utility outages • Significant, widespread tree damage • Essential services delays; significant delays for emergency responders • Significant damage to buildings and property including boats, sheds, RVs, small planes • Increased risk of serious injury from flying or falling debris or collapsing structures/trees • Some critical infrastructure damage
Extreme • Very dangerous and/or impassable travel routes • Prolonged, widespread travel disruption including vehicles blown around or destroyed • Prolonged, widespread utility/power outages • Transmission/utility tower collapse • Stands of trees (forests, orchards, parks) flattened/destroyed • Prolonged essential services disruption • Homes/buildings destroyed • High risk of serious injury from flying/falling debris or collapsing structures/trees • Major agriculture/livestock losses • Critical infrastructure compromised/destroyed; supply chain impacted
Australia In
Australia, tornado warnings are issued by regional offices of the
Bureau of Meteorology (BOM) based in
Melbourne Docklands,
Adelaide,
Darwin,
Perth and
Brisbane. BOM-issued tornado warnings are outlined as either a broad-based warning, covering expected impacts within a weather reporting area, or as a detailed warning, when a thunderstorm is within weather-watch radar range and includes a map depicting any existing thunderstorms and the forecast direction of movement for up to 60 minutes. Warnings are disseminated to the public through terrestrial and online media outlets, and through activation of
Emergency Alert Australia to distribute the alert to local broadcast media (led by the
Standard Emergency Warning Signal tone),
SMS messaging and automated landline phone calls. Tornado Alert sirens and Fire Tornado Alert sirens part of the Emergency Alert Australia plan, HHEM His Highness Emergency Management plan, Emergency Management Australia plan, HH government plan and the Australian Government plan. ==Related warnings and alerts==