View source for Tornado warning

{{Short description|Weather warning indicating imminent danger of tornadoes}}
{{Over-quotation|date=December 2019}}
[[File:NapervilleWoodridgeGraphic.jpg|thumb|An example of a tornado warning polygon issued by the National Weather Service]]
A '''tornado warning''' ([[Specific Area Message Encoding|SAME]] code: TOR) is a public warning that is issued by [[weather forecasting]] agencies to an area in the direct path of a [[tornado]], or a [[Thunderstorm#Severe thunderstorms|severe thunderstorm]] capable of [[Tornadogenesis|producing]] one, and advises individuals in that area to [[Tornado preparedness|take cover]]. Modern weather surveillance technology such as [[Doppler weather radar]] can detect [[Mesocyclone|rotation in a thunderstorm]], allowing for early warning before a tornado develops. They are also commonly issued based on reported visual sighting of a tornado, [[funnel cloud]], or [[wall cloud]], typically from [[weather spotters]] or the public, but also [[Law enforcement agency|law enforcement]] or local [[emergency management]]. When radar is unavailable or insufficient, such [[ground truth]] is crucial. In particular, a tornado can develop in a gap of radar coverage, of which there are [[NEXRAD#Coverage gaps|several known]] in the [[United States]].

A '''warning''' should not be confused with a [[tornado watch]], issued in the [[United States]] by the [[Storm Prediction Center]] (SPC) and in other countries by applicable regional forecasting agencies or national severe weather guidance centers, which only indicates that conditions are favorable for the formation of tornadoes. Although a tornado warning is generally a higher alert level than a tornado watch, in the U.S., it can be surpassed by a higher-level alert—structured as wording that can be added to the official warning product—to warn the public of intense tornadoes affecting a densely populated area.

A tornado watch is not required for a warning to be issued; tornado warnings are occasionally issued when a tornado watch is not active (i.e. when a severe thunderstorm watch is active, or when no watches are in effect), if a severe thunderstorm develops and has a confirmed tornado or strong rotation.

==History in the United States==
=== Early history ===
{{See also|History of tornado research|1948 Tinker Air Force Base tornadoes}}
In April 1899, the ''[[Chicago Tribune]]'' wrote to the [[National Weather Service|United States Weather Bureau]] via a news article posing the question on why [[tornado warning]]s are not sent out via [[telegraphs]] or even the [[telephone]] to warn the local population in the path. Cleveland Abbe responded by saying "it is certain that if any such arrangement were possible, the Weather Bureau would have done this many years ago" along with "we must remember that the destructive areas of tornadoes, and even of thunderstorms, are so small that the chance of being injured is exceedingly slight" and that "we do not attempt to prevent that which is inevitable". They also wrote that the change of being injured by a tornado is "one in ten thousand years".<ref>{{cite journal |last1=Abbe |first1=Cleveland |author1-link=Cleveland Abbe |title=The Prediction of Tornadoes and Thunderstorms |journal=[[Monthly Weather Review]] |date=April 1899 |volume=27 |issue=4 |pages=159–160 |doi=10.1175/1520-0493(1899)27[159:TPOTAT]2.0.CO;2 |publisher=[[National Weather Service|United States Weather Bureau]] (original) / [[American Meteorological Society]] (modern)|doi-access=free }}</ref>

In June 1899, U.S. Weather Bureau [[Oklahoma]] section director J. I. Widmeyer published that long-range forecasters in Oklahoma were sounding "unnecessary tornado alarms" due to "ignorant predictions" to residents in Oklahoma and that they were causing "frightened men, women, and children" to take shelter, despite no tornadoes occurring. Cleveland Abbe added on to the publication by Widmeyer saying, "it is unnecessary to resort to the caves and cellars, or to stop our ordinary avocations for fear of a tornado, until we see the cloud in the distance, or are positively certain that one is about to pass near us".<ref>{{cite journal |last1=Widmeyer |first1=J. I. |last2=Abbe |first2=Cleveland |author2-link=Cleveland Abbe |title=Unnecessary Tornado Alarms |journal=[[Monthly Weather Review]] |date=June 1899 |volume=27 |issue=6 |pages=255 |doi=10.1175/1520-0493(1899)27[255c:UTA]2.0.CO;2 |publisher=[[National Weather Service|United States Weather Bureau]] (original) / [[American Meteorological Society]] (modern)|doi-access=free }}</ref>

In April 1908, the U.S. Weather Bureau published several replies regarding a question posed to the Weather Bureau on: ''How can we protect against tornadoes?''.<ref name="Protect1908">{{cite journal |title=Can We Protect Against Tornadoes ? |url=https://archive.org/details/sim_monthly-weather-review_1908-04_36_4/page/100 |journal=[[Monthly Weather Review]] |date=April 1908 |volume=36 |issue=4 |pages=101–102 |doi=10.1175/1520-0493(1908)36<101:CWPAT>2.0.CO;2 |publisher=[[National Weather Service|United States Weather Bureau]] / [[American Meteorological Society]] (in modern day)|bibcode=1908MWRv...36..101. |doi-access=free }}</ref>
*Lieutenant [[John Park Finley]] responded with "the best we can do is to watch the distant tornado, and if it seems to approach us then move away toward the left; so far as we have learned, this still continues to be the best rule".<ref name="Protect1908"/>
*The Chief of the Weather Bureau responded with the idea to establish a warning system by surrounding a city at a distance of {{convert|4|mi|km|abbr=on}} with wires hooked up with alarms. That way, a warning can be given to the city for an impending tornado. The wire system would detect sudden pressure differences, if wires were twisted, or if wires were short circuited. It was also stated that at a distance of four miles from the city, the tornado "would be unable to reach the city from any direction without giving us an alarm".<ref name="Protect1908"/>
*[[Cleveland Abbe]] responded by saying the idea of a wire-based system around a city is not practical as well as how tornadoes are very infrequent. Abbe ended by saying that "the mere forewarning of a tornado is no protection against its coming" and that it would be wiser to "spend your money to protect yourself against diseases, accidents, lightning, ect…".<ref name="Protect1908"/>

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.<ref name="stormwarning3"/> 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.<ref>{{cite web|title=The Online Tornado FAQ|url=http://www.spc.noaa.gov/faq/tornado/#Forecasting|author=Roger Edwards|publisher=[[Storm Prediction Center]]|access-date=July 6, 2009|author-link=Roger Edwards (meteorologist)}}</ref> 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, Missouri|St. Louis]]; after garnering press coverage for their successful prediction of past tornadoes, AMS representatives decided to open the presentation to the public.<ref name="stormwarning3"/>

The first official tornado forecast 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 [[National Weather Service|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&nbsp;p.m., forecasters from [[Will Rogers World Airport|Will Rogers Airport]] sent a warning to Tinker that the storm encroaching the city was producing wind gusts of {{convert|92|mph|kph}} and a "Tornado South on Ground Moving NE!" Base personnel received an alert written by the staff sergeant on duty with Miller; the twister struck Tinker several minutes later around 10:00&nbsp;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.<ref name="stormwarning1">{{cite book|title=Storm Warning: The Story of a Killer Tornado|author=Nancy Mathis|publisher=[[Simon & Schuster|Touchstone]]|pages=[https://archive.org/details/stormwarningstor00math/page/41 41–43]|year=2007|isbn=978-0-7432-8053-2|url=https://archive.org/details/stormwarningstor00math/page/41}}</ref>

Following an inquiry the next day before a tribunal of five generals who traveled to Tinker from [[Washington, D.C.]], who ruled that the March 20 tornado was an "act of God ... not forecastable given the present state of the art", base commander Gen. Fred Borum tasked Miller and Fawbush to follow up on the board's suggestion to consider methods of forecasting tornadic thunderstorms. Over the next three days, Miller and Fawbush studied reports and charts from previous tornado events to determine the atmospheric conditions favorable for the development of tornadic activity, in an effort to predict such events with some degree of accuracy. At the time, there had not been studies on how tornadoes formed; however, military radars were being adapted for forecasting use, allowing forecasters to see the outlines of storms but not their internal attributes such as rotation. Miller and Fawbush's findings on atmospheric phenomenon present in past outbreaks would aid in their initial forecast, as the day's surface and upper-air analysis charts determined the same conditions present on March 20 were present on the 25th, concluded that central Oklahoma would have the highest risk for tornadoes during the late-afternoon and evening.<ref name="stormwarning1"/>

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&nbsp;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&nbsp;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.<ref name="stormwarning1"/><ref name="stormwarning2">{{cite book|title=Storm Warning: The Story of a Killer Tornado|author=Nancy Mathis|publisher=Touchstone|pages=[https://archive.org/details/stormwarningstor00math/page/44 44–47]|year=2007|isbn=978-0-7432-8053-2|url=https://archive.org/details/stormwarningstor00math/page/44}}</ref>

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.<ref name="stormwarning2"/> 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 [[Signal Corps (United States Army)|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.<ref>{{cite journal |last1=Bates |first1=F. C. |title=Severe Local Storm Forecasts and Warnings and the General Public |journal=Bulletin of the American Meteorological Society |date=1 July 1962 |volume=43 |issue=7 |pages=288–291 |doi=10.1175/1520-0477-43.7.288 |bibcode=1962BAMS...43..288B |doi-access=free }}</ref><ref>{{cite journal |last1=Coleman |first1=Timothy |last2=Knupp |first2=Kevin |last3=Spann |first3=James |last4=Elliott |first4=J |last5=Peters |first5=Brian |title=The History (and Future) of Tornado Warning Dissemination in the United States |journal=Bulletin of the American Meteorological Society |year=2011 |volume=92 |issue=5 |pages=567–582|doi=10.1175/2010BAMS3062.1 |bibcode=2011BAMS...92..567C |doi-access=free }}</ref> 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 [[1947_Glazier–Higgins–Woodward_tornado_outbreak|Glazier–Higgins–Woodward tornadoes]] in April 1947) having death tolls well over 100.<ref name="stormwarning3">{{cite book|title=Storm Warning: The Story of a Killer Tornado|author=Nancy Mathis|publisher=Touchstone|pages=[https://archive.org/details/stormwarningstor00math/page/47 47–53]|year=2007|isbn=978-0-7432-8053-2|url=https://archive.org/details/stormwarningstor00math/page/47}}</ref>

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]]).<ref name="stormwarning3"/>

Even after the U.S. Weather Bureau lifted their ban on tornado warnings, the [[Federal Communications Commission]] continued to ban television and radio outlets from broadcasting tornado warnings on-air for the same reasoning cited in the Bureau's abolished ban. Broadcast media followed this ban until 1954, when meteorologist [[Harry Volkman]] broadcast the first televised tornado warning over WKY-TV (now [[KFOR-TV]]) in [[Oklahoma City]], due to his belief that the banning of tornado warnings over broadcast media cost lives. Through an alert issued by the USAF Severe Weather Warning Center, Volkman opted to interrupt regular programming to warn viewers of a reported tornado approaching the Oklahoma City area; although station management and U.S. Weather Bureau officials were displeased with his move, WKY-TV received numerous telephone calls and letters thanking Volkman for the warning.<ref>{{cite web|title=Tulsa TV Weather|url=http://tulsatvmemories.com/weather.html|website=Tulsa TV Memories|access-date=February 11, 2012}}</ref><ref>{{cite journal |title=The History (and Future) of Tornado Warning Dissemination in the United States|author=Timothy A. Coleman|date=May 2011|doi=10.1175/2010BAMS3062.1|volume=92|journal=[[American Meteorological Society|Bulletin of the American Meteorological Society]]|issue=5|pages=567–582|bibcode=2011BAMS...92..567C|doi-access=free}}</ref><ref name="stormwarning4">{{cite book|title=Storm Warning: The Story of a Killer Tornado|author=Nancy Mathis|publisher=Touchstone|pages=[https://archive.org/details/stormwarningstor00math/page/85 85]|year=2007|isbn=978-0-7432-8053-2|url=https://archive.org/details/stormwarningstor00math/page/85}}</ref>

<!--=== Tornado Warning program ===

=== Criticism -->

==Definition==
{{See also|Tornado preparedness}}
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
* [[Wall cloud|strong low-level rotation]] is indicated by [[weather radar]],<ref name="Definition"/> or
* a [[waterspout]] is headed for [[Landfall (meteorology)|landfall]].<ref name="Definition"/>

A ''tornado warning'' means there is immediate danger for the warned area and immediate surrounding locations from the severe thunderstorm producing (or likely to produce) a tornado, if not from the relatively narrow tornado itself. Persons in the path of a warned storm are urged to immediately seek shelter in a basement, [[storm cellar|cellar]], [[safe room]] or a sturdy above-ground room in the center section of a home or building (such as a [[bathroom]] or [[closet]]). In addition to the likelihood of a tornado, generally (but not always), a tornado warning also indicates that the parent severe thunderstorm has the likelihood of producing [[downburst|straight-line winds]] and/or large [[hail]] exceeding regional severe criterion as well as intense [[lightning]], heavy rainfall and/or, through associated rain accumulations, [[flash flood]]ing. (The classifiable criteria for a severe thunderstorm vary by country; e.g., in the United States, a thunderstorm is considered severe if it produces winds exceeding {{convert|58|mph|kph|disp=sqbr|abbr=on}} and/or hailstones {{convert|1|in|cm|spell=in|disp=sqbr}} or larger in diameter.)<ref name="Example2"/> A tornado warning therefore implies that it is also a [[severe thunderstorm warning]]. Conversely, a severe thunderstorm warning, either in its entirety or sectionally, can be replaced by a tornado warning if a storm exhibits credible characteristics of tornadogenesis from radar and ground observations.<ref name="Example2"/>

Tornado warnings are issued by weather forecasting agencies based on [[tornado vortex signature|mesocyclone]] and [[tornado debris signature|debris]] signatures identifiable on [[Weather radar|Doppler weather radar]], and/or [[ground truth]] from [[storm spotting|storm spotters]] of signs of tornadogenesis (including wall clouds, funnel clouds and low-level mesocyclonic rotation) and of observed tornadoes. [[Skywarn]], a U.S.-based international spotter program that provides training to citizens on how to spot severe weather phenomena, is offered by forecasting agencies in several countries including the [[National Weather Service]] (NWS) in the United States.<ref>{{cite web|title=SKYWARN|url=http://www.ict-skywarn.org/|website=[[Skywarn]]|access-date=January 13, 2011|archive-date=July 18, 2011|archive-url=https://web.archive.org/web/20110718204733/http://ict-skywarn.org/|url-status=dead}}</ref> 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.<ref name="Groundtruth3"/> Other spotter groups such as the [[Amateur Radio Emergency Service]], news media, local [[law enforcement agencies]], [[emergency management]] organizations, [[Cooperative Observer Program|cooperative observers]]; members of the general public also relay information to forecasting agencies for ground truthing.<ref name="Groundtruth4"/>

When a warning is issued, people in the storm's path are advised to use local broadcast media, [[weather radio]], [[mobile app|weather app]] alert notifications and/or [[SMS]] notifications to receive warnings and updated storm information. In some tornado-prone regions, [[civil defense siren|tornado sirens]], if present, are usually activated within the specified warning region or an entire municipality—varying in coverage based on if a local siren network maintains a sector-organized relay structure—to inform people that a tornado has been sighted or may be forming nearby. Because sirens are generally difficult to hear indoors, residents are advised against completely depending on them as a method of receiving warnings. Local police or fire departments may dispatch crews not assigned to an existing emergency call to travel within a designated area to warn residents to take tornado safety precautions if sirens are disabled due to technical problems or are not present, while [[Auto dialer|automated phone calls]] may be made to residents for the same purpose in some areas should such disruptions occur.<ref>{{cite web|title=Severe Weather Awareness Week |url=http://www.crh.noaa.gov/mpx/?n=swaw |author=National Weather Service Twin Cities, MN |publisher=National Oceanic and Atmospheric Administration |date=April 22, 2010 |access-date=December 15, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100426135517/http://www.crh.noaa.gov/mpx/?n=swaw |archive-date=April 26, 2010 }}</ref>

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|lc=y}} (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.<ref>{{cite web|title=Tornado Warnings Infographic|url=http://mattcuttsalerts.com/tornado-warnings/|website=Matt Cutt's Alerts|access-date=July 18, 2013|url-status=usurped|archive-url=https://web.archive.org/web/20130716172215/http://mattcuttsalerts.com/tornado-warnings/|archive-date=July 16, 2013}}</ref> 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.{{Citation needed|date=April 2010}}

===Regional basis===
====United States====
In the United States, tornado warnings are issued by local [[List of National Weather Service Weather Forecast Offices|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 outbreak|severe thunderstorm]]/[[tornado outbreak]] is expected or, particularly from November to March, when strong tornadoes are forecast to occur after nightfall)
#[[Tornado watch|Tornado Watch]]
#[[Particularly Dangerous Situation|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 <ref name=":0">{{Cite web|title=Impact-Based Warning Content|url=https://training.weather.gov/wdtd/courses/rac/warnings/IBW-content/story.html|access-date=2021-05-11|website=training.weather.gov}}</ref>
#[[Tornado emergency|Tornado Emergency]]<ref name=":0" />

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 [[National Oceanic and Atmospheric Administration|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.<ref name="Dissemination"/> Warnings for tornadoes and severe thunderstorms are outlined in [[polygon]]al shapes for map-based weather hazard products distributed to the main agency, individual forecast office websites and the Storm Prediction Center (including open-source [[API]]s 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 [[County (United States)|counties]], [[Parish (administrative division)|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.<ref name="Storm-based"/> SPC and NWS products as well as [[First Warning|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.)

The NWS has the option of adding intensified wording to tornado warning products and update statements issued as a Severe Weather Statement (SVS)—"particularly dangerous situation" (PDS) or "tornado emergency"—when a severe threat to human life and considerable or catastrophic property damage from a visually observed or radar-detected large tornado is imminent or ongoing. Tornado emergencies and PDS tornado warnings—which, when warranted, are usually issued when a large tornado is expected to impact a populated area—typically include action statements indicating that the tornado is extremely dangerous and life-threatening, and capable of significant if not total property destruction and severe injury or death from the intense winds and projectile [[debris]]; tornado warnings that have the "tornado emergency" wording typically incorporate a combination of the emergency and PDS phrasing above the text's basis (or "hazard") statement.<ref name="nws-svrrsrcs">{{cite web|title=NATIONAL WEATHER SERVICE INSTRUCTION 10-511: WFO SEVERE WEATHER PRODUCTS SPECIFICATION|url=https://www.nws.noaa.gov/directives/sym/pd01005011curr.pdf|website=National Weather Service Analyze, Forecast, and Support Office|publisher=National Oceanic and Atmospheric Administration|date=April 15, 2020|access-date=March 7, 2021}}</ref>

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, Kansas|Wichita]] and [[Topeka, Kansas]], and [[Springfield, Missouri|Springfield]], [[St. Louis, Missouri|St. Louis]] and [[Kansas City, Missouri|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:<ref name=IBW>{{cite web|title=Impact Based Warnings|url=http://www.weather.gov/impacts/|website=[[National Weather Service]]|publisher=[[National Oceanic and Atmospheric Administration]]|date=2014|access-date=March 12, 2014}}</ref><ref name="nws-ibwrsrcs">{{cite web|title=National Weather Service Product Description Document (PDD): National Impact Based Warnings (IBW)|url=https://nws.weather.gov/products/PDD/National_IBW_pdd_4_17%20.pdf|website=National Weather Service Analyze, Forecast, and Support Office|publisher=National Oceanic and Atmospheric Administration|date=April 17, 2020|access-date=March 7, 2021}}</ref>
* 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 [[tornado vortex signature|intense velocity couplet]] and/or [[tornado debris signature|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|Lassen County]], California, which was being affected by the [[Loyalton Fire]].<ref>{{cite news|url=https://www.usatoday.com/story/news/weather/2020/08/16/fire-tornado-loyalton-fire-california-warning/5597082002/|title=What is a fire tornado? 'Extreme fire activity' sparks rare weather warning at Loyalton Fire near Reno.|first=Jordan|last=Culver|work=USA Today|date=August 17, 2020|access-date=October 15, 2020}}</ref><ref>[https://www.sacbee.com/news/weather-news/article244993335.html A ‘fire tornado’ warning? Weather service issues what could be a first at California blaze]</ref><ref>{{cite web|url=https://forecast.weather.gov/product.php?site=rev&issuedby=REV&product=TOR|title=Tornado Warning|publisher=[[National Weather Service]]|date=August 15, 2020|access-date=October 15, 2020|archive-url=https://archive.today/20200815232312/https://forecast.weather.gov/product.php?site=rev&issuedby=REV&product=TOR|archive-date=August 15, 2020|url-status=dead}}</ref>

In April 2023, [[United States Senate|U.S. Sen.]] [[Roger Wicker]] ([[Republican Party (United States)|R]]–[[Mississippi|MS]]) introduced the [[TORNADO Act|Tornado Observation Research Notification and Deployment to Operations (TORNADO) Act]].<ref>{{cite web |date=2023-04-26 |title=TORNADO Act introduced by Wicker, Hyde-Smith and colleagues |url=https://www.vicksburgpost.com/2023/04/26/tornado-act-introduced-by-wicker-hyde-smith-and-colleagues/ |access-date=26 April 2023 |publisher=The Vicksburg Post}}</ref> 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]].<ref>{{Cite web |last=Kanost |first=Tyler |date=2022-03-15 |title=Members of Congress want improvements to National Weather Service alert system |url=https://www.weareiowa.com/article/weather/severe-weather/tornado-act-congress-legislation-national-weather-service-alerts/524-285d4475-ffe1-4a14-a8f9-03f6b0dd74f7 |access-date=2023-04-27 |website=weareiowa.com |language=en-US}}</ref>

====Canada====
In [[Canada]], [[Environment and Climate Change Canada]] issues tornado warnings through regional [[Meteorological Service of Canada|Meteorological Service]] offices based in [[Vancouver]], [[Edmonton]], [[Winnipeg]], [[Toronto]], [[Montreal]] and [[Dartmouth, Nova Scotia|Dartmouth]] for specified municipalities and [[Census geographic units of Canada|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).<ref name="Canada"/><ref>{{cite web|title=Criteria for public weather alerts|url=https://www.canada.ca/en/environment-climate-change/services/types-weather-forecasts-use/public/criteria-alerts.html#tornado|website=Environment and Climate Change Canada|date=26 July 2010 |access-date=March 16, 2021}}</ref>

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|National Public Alerting System (Alert Ready)]] ({{langx|fr|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 [[Ontario|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.<ref>{{cite press release|title=Red Alert System to warn Ontarians|url=https://news.ontario.ca/en/release/677/red-alert-system-to-warn-ontarians|publisher=[[Office of the Ontario Solicitor General]]|date=May 6, 2008|access-date=March 6, 2021}}</ref>

====Australia====
In [[Australia]], tornado warnings are issued by regional offices of the [[Bureau of Meteorology]] (BOM) based in [[Docklands, Victoria|Melbourne Docklands]], [[Adelaide]], [[Darwin, Northern Territory|Darwin]], [[Perth, Western Australia|Perth]] and [[Brisbane]].<ref name="auto">{{Cite web|url=http://www.bom.gov.au/catalogue/warnings/WarningsInformation_SW_STSW.shtml|title=Australian weather and warnings information|website=www.bom.gov.au|language=en|access-date=2017-01-06|archive-url=https://web.archive.org/web/20170107004318/http://www.bom.gov.au/catalogue/warnings/WarningsInformation_SW_STSW.shtml|archive-date=2017-01-07|url-status=dead}}</ref> 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.<ref name="auto"/><ref>{{Cite web|url=http://www.bom.gov.au/weather-services/|title=National Weather Services - Bureau of Meteorology|website=www.bom.gov.au|access-date=2017-01-06}}</ref> 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==
===Tornado alert===
For many years until the early 1980s, an intermediate type of tornado advisory known as a tornado alert was defined by the National Weather Service and issued by the agency's local forecast offices, indicating that tornado formation was imminent. In theory, tornado alerts covered situations such as visible rotation in clouds and certain other phenomena which are portents of funnel cloud formation. The National Weather Service's use of this advisory began to decline after 1974, although it was still listed on public information materials issued by various media outlets, local NWS offices and other entities for another decade or so.

The criteria which called for tornado alerts in the past now generally result in a tornado warning with clarifying verbiage specifying that the warning was issued because rotation was detected in one way or another, that a [[wall cloud]] has formed or a tornado has been spotted or detected. The preferred response to both the tornado alerts and warnings is to take shelter immediately, so distinguishing them could be seen as splitting hairs, especially since storm prediction methods have improved.

The tornado alert was finally eliminated outright because it was made largely obsolete by the advent of [[Doppler weather radar]], which can detect rotational funnel cloud formations earlier than is typically possible by trained spotters and members of the public. With fewer false-positives, radar also helped reduce public confusion over storm types, strengths and precise locations. The last tornado alert to be officially issued was discussed in earnest following the [[1974 Super Outbreak]].

===Tornado emergency===
{{Main|Tornado emergency}}
The National Weather Service has the option of issuing a [[tornado emergency]], a severe weather statement with unofficial, enhanced wording that is disseminated when reliable sources confirm that a violent tornado is ongoing, that poses a catastrophic risk for damage and threat to human life.<ref>{{cite web |url=https://www.weather.gov/impacts/examples |title=Impact Based Warning Examples |publisher=[[National Weather Service]] }}</ref> 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 [[1999 Bridge Creek–Moore tornado|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.

==Examples==
{{Listen|filename=NWR audio Greensburg, Kansas tornado May 4, 2007.ogg|title= Greensburg tornado warning|description=NOAA Weather Radio audio of a tornado warning issued for [[Greensburg, Kansas]] on May 4, 2007, Greensburg was struck by an [[2007 Greensburg tornado|EF5 tornado]].}}
{{Listen
 |filename     = TOR.wav
 |title        = Tornado warning South Carolina
 |description  = A tornado warning issued in South Carolina during the [[tornado outbreak of November 27–30, 2016]]
}}


















Below are several examples of a tornado warning issued. The audio files on the right are for Greensburg, Kansas, and upstate South Carolina.<ref>{{cite web |title= IEM :: Valid Time Extent Code (VTEC) App |url= https://mesonet.agron.iastate.edu/vtec/#2018-O-NEW-KDMX-TO-W-0026/USCOMP-N0Q-201806202055 |website= Iowa Environmental Mesonet |publisher= Iowa State University |access-date= June 21, 2018}}</ref>



<pre>


Tornado Warning
KSC111-127-197-160300-
/O.NEW.KTOP.TO.W.0043.190816T0233Z-190816T0300Z/

BULLETIN - EAS ACTIVATION REQUESTED
Tornado Warning 
National Weather Service Topeka KS
933 PM CDT Thu Aug 15 2019

The National Weather Service in Topeka has issued a

* Tornado Warning for...
  Northeastern Morris County in east central Kansas...
  Southwestern Wabaunsee County in east central Kansas...
  Northwestern Lyon County in east central Kansas...

* Until 1000 PM CDT.

* At 932 PM CDT, a confirmed tornado was located 7 miles east of Alta
  Vista, moving southeast at 20 mph.

  HAZARD...Damaging tornado and golf ball size hail.

  SOURCE...Weather spotters confirmed tornado.

  IMPACT...Flying debris will be dangerous to those caught without
           shelter. Mobile homes will be damaged or destroyed.
           Damage to roofs, windows, and vehicles will occur.  Tree
           damage is likely.

* This tornadic thunderstorm will remain over mainly rural areas of
  northeastern Morris, southwestern Wabaunsee and northwestern Lyon
  Counties.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

To repeat, a tornado is on the ground. TAKE COVER NOW! Move to a
basement or an interior room on the lowest floor of a sturdy
building. Avoid windows. If you are outdoors, in a mobile home, or in
a vehicle, move to the closest substantial shelter and protect
yourself from flying debris.

&&

LAT...LON 3886 9647 3898 9636 3887 9618 3881 9624
      3869 9613 3863 9633
TIME...MOT...LOC 0232Z 309DEG 18KT 3882 9635

TORNADO...OBSERVED
HAIL...1.75IN

$$

Gargan

also
�
712
WFUS53 KGRR 250022
TORGRR
MIC081-250045-
/O.NEW.KGRR.TO.W.0004.230825T0022Z-230825T0045Z/

BULLETIN - EAS ACTIVATION REQUESTED
Tornado Warning
National Weather Service Grand Rapids MI
822 PM EDT Thu Aug 24 2023

The National Weather Service in Grand Rapids has issued a

* Tornado Warning for...
  Central Kent County in southwestern Michigan...

* Until 845 PM EDT.

* At 821 PM EDT, a severe thunderstorm capable of producing a tornado
  was located near Grand Rapids, moving southeast at 40 mph.

  HAZARD...Tornado and quarter size hail.

  SOURCE...Radar indicated rotation.

  IMPACT...Flying debris will be dangerous to those caught without
           shelter. Mobile homes will be damaged or destroyed.
           Damage to roofs, windows, and vehicles will occur.  Tree
           damage is likely.

* This dangerous storm will be near...
  Grand Rapids, Kentwood, East Grand Rapids, and Rockford around 825
  PM EDT.
  Gerald R. Ford International Airport around 830 PM EDT.
  Lowell around 835 PM EDT.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TAKE COVER NOW! Move to a basement or an interior room on the lowest
floor of a sturdy building. Avoid windows. If you are outdoors, in a
mobile home, or in a vehicle, move to the closest substantial shelter
and protect yourself from flying debris.

&&

LAT...LON 4315 8567 4309 8531 4281 8531 4282 8535
      4300 8579
TIME...MOT...LOC 0021Z 299DEG 35KT 4304 8564

TORNADO...RADAR INDICATED
MAX HAIL SIZE...1.00 IN

$$

DUKE


227 
WFUS51 KRLX 021515
TORRLX
WVC007-013-015-019-039-067-087-021545-
/O.NEW.KRLX.TO.W.0009.240402T1515Z-240402T1545Z/

BULLETIN - EAS ACTIVATION REQUESTED
Tornado Warning
National Weather Service Charleston WV
1115 AM EDT Tue Apr 2 2024

The National Weather Service in Charleston West Virginia has issued a

* Tornado Warning for...
  Southeastern Calhoun County in north central West Virginia...
  Western Nicholas County in southeastern West Virginia...
  Northeastern Kanawha County in central West Virginia...
  Southwestern Braxton County in north central West Virginia...
  Southern Roane County in central West Virginia...
  Clay County in north central West Virginia...
  Northwestern Fayette County in southeastern West Virginia...

* Until 1145 AM EDT.

* At 1115 AM EDT, severe thunderstorms capable of producing both
  tornadoes and extensive straight line wind damage were located
  along a line extending from 6 miles east of Kenna to near Coal Fork
  to 7 miles southwest of Marmet, moving east at 70 mph.

  HAZARD...Tornado.

  SOURCE...Radar indicated rotation.

  IMPACT...Flying debris will be dangerous to those caught without 
           shelter. Mobile homes will be damaged or destroyed. 
           Damage to roofs, windows, and vehicles will occur.  Tree 
           damage is likely.

* These dangerous storms will be near...
  Chesapeake, Marmet, Belle, Clendenin, Cedar Grove, East Bank, 
  Glasgow, Pratt, Coal Fork, and Pinch around 1120 AM EDT.
  Montgomery, Smithers, Powellton, Amma, and Glen around 1125 AM 
  EDT.
  Clay, Gauley Bridge, Wallback, and Big Otter around 1130 AM EDT.

Other locations impacted by these tornadic storms include Widen,
Nebo, Frametown, Strange Creek, Wilsie, Bickmore, Tariff, Procious,
Servia, and Muddlety.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TAKE COVER NOW! Move to a basement or an interior room on the lowest
floor of a sturdy building. Avoid windows. If you are outdoors, in a
mobile home, or in a vehicle, move to the closest substantial shelter
and protect yourself from flying debris.

Motorists should not take shelter under highway overpasses. If you
cannot safely drive away from the tornado, as a last resort, either
park your vehicle and stay put, or abandon your vehicle and lie down
in a low lying area and protect yourself from flying debris.

&&

LAT...LON 3818 8162 3836 8154 3861 8153 3861 8152
      3868 8153 3871 8079 3843 8074 3816 8088
      3816 8160
TIME...MOT...LOC 1515Z 266DEG 71KT 3866 8155 3837 8154 3815 8164 

TORNADO...RADAR INDICATED
MAX HAIL SIZE...<.75 IN

$$

30

</pre>

Below is an example of tornado warning for a [[pyrocumulonimbus]] capable of causing a [[fire tornado]].<ref>{{Cite web |url=https://forecast.weather.gov/product.php?site=rev&issuedby=REV&product=TOR |title=Tornado Warning |access-date=2020-08-15 |archive-date=2020-08-15 |archive-url=https://archive.today/20200815232312/https://forecast.weather.gov/product.php?site=rev&issuedby=REV&product=TOR |url-status=live }}</ref> This was the first time a tornado warning was issued for an event of this type.

<pre>
000
WFUS55 KREV 152135
TORREV
CAC035-152230-
/O.NEW.KREV.TO.W.0001.200815T2135Z-200815T2230Z/

BULLETIN - EAS ACTIVATION REQUESTED
Tornado Warning
National Weather Service Reno NV
235 PM PDT Sat Aug 15 2020

The National Weather Service in Reno has issued a

* Tornado Warning for...
  Southeastern Lassen County in northern California...

* Until 330 PM PDT.

* At 228 PM PDT, a pyrocumulonimbus from the Loyalton Wildfire is
  capable of producing a fire induced tornado and outflow winds in
  excess of 60 mph was located south of Chilcoot, and is nearly
  stationary.

  HAZARD...Tornado.

  SOURCE...Radar indicated rotation.

  IMPACT...Extreme fire behavior with strong outflow winds capable
           of downing trees and starting new fires. This is and
           extremely dangerous situation for fire fighters.

* This tornadic pyrocumulonimbus will remain over mainly rural areas
  of southeastern Lassen County in the vicinity of the fire.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TAKE COVER NOW! Move to a basement or an interior room on the lowest
floor of a sturdy building. Avoid windows. If you are outdoors, in a
mobile home, or in a vehicle, move to the closest substantial shelter
and protect yourself from flying debris.

&&

LAT...LON 3975 12012 3972 12007 3970 12014 3971 12015
      3973 12015
TIME...MOT...LOC 2128Z 240DEG 0KT 3972 12013

TORNADO...RADAR INDICATED
HAIL...<.75IN

$$

WH

</pre>

Below is an example of an Environment Canada-issued tornado warning for southeastern [[Saskatchewan]]. As with all emergency warnings in Canada, a French-language version would immediately follow.

<pre>
344
WFCN13 CWWG 262334
TORNADO WARNING
UPDATED BY ENVIRONMENT CANADA
AT 5:34 PM CST TUESDAY 26 JUNE 2012.
----
TORNADO WARNING FOR:
      R.M. OF WHEATLANDS INCLUDING MORTLACH AND PARKBEG
      R.M. OF CARON INCLUDING CARONPORT AND CARON
      R.M. OF MOOSE JAW INCLUDING PASQUA AND BUSHELL PARK
      CITY OF MOOSE JAW.

TORNADO WARNING ENDED FOR:
      R.M. OF RODGERS INCLUDING CODERRE AND COURVAL
      R.M. OF HILLSBOROUGH INCLUDING CRESTWYND AND OLD WIVES LAKE.

----
==DISCUSSION==
AT 5:30 PM CST, PUBLIC REPORTS A  TORNADO CURRENTLY ON THE
GROUND WEST OF MOOSE JAW. RADAR INDICATES THE SEVERE THUNDERSTORM
ASSOCIATED WITH THIS TORNADO IS CURRENTLY JUST SOUTH OF MORTLACH AND
IS SLOWLY TRACKING NORTHEASTWARDS TOWARDS THE CITY OF MOOSE JAW.

</pre>

==See also==
{{Wikisource category}}
{{portal|Tornadoes}}
* [[Severe weather terminology (United States)]]
* [[Emergency Broadcast System]]
* [[Emergency Alert System]]
* [[Microburst]]
* [[Emergency Communication System]]

==References==
{{Reflist|refs=
<!--<ref name="Example">{{cite web|title=Tornado Warning|url=http://mesonet.agron.iastate.edu/vtec/#2007-O-NEW-KDDC-TO-W-0025|author=Michael E. Umscheid|website=Iowa Environmental Mesonet NWS Product Archive|date=May 4, 2007|access-date=April 10, 2010}}</ref>-->
<ref name="Example2">{{cite web|title=Tornado Warning|url=http://mesonet.agron.iastate.edu/vtec/#2008-O-NEW-KICT-TO-W-0049|author=Paul Howerton|website=Iowa Environmental Mesonet NWS Product Archive|date=June 12, 2008|access-date=January 10, 2010}}</ref>
<!--<ref name="Training">{{cite paper|title=Storm Fury on the Plains|author=Chance Hayes|series=Storm spotter training presentations, NWS Wichita, Kansas|location=Salina, Kansas|date=February 23, 2009}}</ref>-->
<ref name="Definition">{{cite web|title=Tornado Warning|url=http://www.nws.noaa.gov/glossary/index.php?word=Tornado+Warning|website=NOAA National Weather Service Glossary|access-date=January 10, 2010}}</ref>
<ref name="Groundtruth3">{{cite web|type=Report|author=Andy Wood|title=Spotter Report Data Quality|url=http://www.wdtb.noaa.gov/modules/spotters/player.html|page=3|publisher=Warning Decision Training Branch|date=November 10, 2008|access-date=January 10, 2010|archive-date=March 11, 2010|archive-url=https://web.archive.org/web/20100311190906/http://wdtb.noaa.gov/modules/spotters/player.html|url-status=dead}}</ref>
<ref name="Groundtruth4">{{cite web|type=Report|title=Spotter Report Data Quality|url=http://www.wdtb.noaa.gov/modules/spotters/player.html|author=Andy Wood|publisher=Warning Decision Training Branch|page=4|date=November 10, 2008|access-date=January 10, 2010|archive-date=March 11, 2010|archive-url=https://web.archive.org/web/20100311190906/http://wdtb.noaa.gov/modules/spotters/player.html|url-status=dead}}</ref>
<ref name="Canada">{{cite web|title=Prairie and Northern Region Weather Watch and Weather Warning Criteria: Tornado warning|url=http://www.pnr-rpn.ec.gc.ca/air/severewthr/warning.en.html|publisher=[[Environment Canada]]|access-date=January 10, 2010|url-status=dead|archive-url=https://web.archive.org/web/20020220011348/http://www.pnr-rpn.ec.gc.ca/air/severewthr/warning.en.html|archive-date=February 20, 2002}}</ref>
<ref name="Dissemination">{{cite web|title=NWS Dissemination Services|url=http://www.nws.noaa.gov/om/disemsys.shtml|publisher=NWS Office of Climate, Water, and Weather Services|access-date=January 10, 2010}}</ref>
<ref name="Storm-based">{{cite web|title=Storm-Based Warnings: Why Storm-Based Warnings?|url=http://www.weather.gov/sbwarnings/|publisher=NOAA Warning Decision Training Branch|date=February 26, 2008|access-date=January 11, 2010|archive-url=https://web.archive.org/web/20100124141737/http://www.weather.gov/sbwarnings/|archive-date=2010-01-24|url-status=dead}}</ref>}}

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