A tornado warning (SAME code: TOR) is an alert issued by weather services to warn that severe thunderstorms with tornadoes may be imminent. It can be issued after a tornado or funnel cloud has been spotted by the public, storm chasers, emergency management or law enforcement, or more commonly if there are radar indications of tornado formation. When this happens, the tornado sirens may sound in that area if any sirens are present, informing people that a tornado has been sighted or is forming nearby. The issuance of a tornado warning indicates that residents should take immediate safety precautions. It is a higher level of alert than a tornado watch, but (in the United States) it can be surpassed by an even higher alert known as a tornado emergency.
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 USAF had pioneered tornado forecasting and tornado warnings, mainly due to the U.S. Weather Bureau's strong discouragement/ban on the use of the word "tornado" in forecasts or statements, fearing that it would cause the public to panic if tornadoes were predicted to occur (the side effect of this was that the lack of warning resulted in an increased number of tornado-related fatalities, with some events prior to 1948 such as the Glazier–Higgins–Woodward tornadoes that occurred the previous year having exceeded well over 100 deaths).
In 1950, the Weather Bureau revoked its ban on the usage of the word "tornado" in its weather products, thus allowing public tornado warnings. Chief of Bureau F.W. Reichelderfer officially lifted the ban on issuing tornado warnings 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."
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.
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 local offices thereof. A tornado alert indicated that tornado formation was imminent and in theory covered situations such as visible rotation in clouds and some other phenomena which are portents of funnel formation. The use of this advisory began to decline after 1974, but 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 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 Super Outbreak of April 3 and 4, 1974.
When a large, extremely violent tornado is about to impact a densely populated area, the National Weather Service has the option of issuing a severe weather statement with unofficial, enhanced wording; this is called a tornado emergency. 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 area, causing major damage. 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'.
The levels of severity increase as follows:
- Convective Outlook mentioning tornado potential
- Public Severe Weather Outlook mentioning tornado potential
- Tornado Watch
- Particularly Dangerous Situation Tornado Watch
- Tornado Warning
- Particularly Dangerous Situation Tornado Warning (used by Weather Forecast Offices within the National Weather Service Central Region Headquarters as an intermediate warning in the event that a tornado has been spotted or confirmed, or a significant tornado is expected)
- Tornado Emergency
Tornado warnings can also be intensified by added wording mentioning that the storm is life-threatening, that it is an extremely dangerous situation, that a large, violent and/or destructive tornado is on the ground or is capable of causing significant property damage.
A tornado warning is issued when any of the following conditions has occurred:
- a tornado is reported on the ground, or
- a funnel cloud is reported, or
- strong low-level rotation is indicated by weather radar, or
- a waterspout is headed for landfall.
A tornado warning means there is immediate danger for the warned and immediately surrounding area – if not from the relatively narrow tornado itself, from the severe thunderstorm producing (or likely to produce) it. All in the path of such a storm are urged to take cover immediately, as it is a life-threatening situation. A warning is different from a tornado watch (issued by a national guidance center, the Storm Prediction Center) which only indicates that conditions are favorable for the formation of tornadoes.
Generally (but not always), a tornado warning also indicates that the potential is there for severe straight-line winds and/or large hail from the thunderstorm. A severe thunderstorm warning can be upgraded suddenly to a tornado warning should conditions warrant.
In the United States, local offices of the National Weather Service issue warnings for tornadoes and severe thunderstorms in polygon shapes, which are used to delineate sections of a county, parish or other jurisdiction that the warning covers (which are also referenced in NWS text warning products), based on the projected path of a storm as determined by Doppler radar at the time of the warning's issuance; however, entire counties/parishes are sometimes included in the warning polygon, especially if they encompass a small geographical area. Warnings were issued on a per-county basis prior to October 2007. Storm Prediction Center and National Weather Service products as well as severe weather alert displays used by some television stations highlight tornado warnings with a red polygon or filled county/parish outline.
In Canada, similar criteria are used and warnings are issued by regional offices of the Meteorological Service of Canada of Environment Canada in Vancouver, Edmonton, Winnipeg, Toronto, Montreal and Halifax (in the province of Ontario, Emergency Management Ontario recently began issuing red alerts for areas of the province that are already under an Environment Canada-issued tornado warning; these red alerts sometimes override the tornado warning if local government or media are participating in the program).
Tornado warnings are generated via AWIPS then disseminated through various communication routes accessed by the media and various agencies, on the internet, to NOAA satellites, and on NOAA Weather Radio. Tornado sirens are also usually activated for the affected areas if present.
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 to about 15 minutes (in some cases, to more than an hour's warning of impending tornadoes). The U.S. 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.
The SKYWARN program, which teaches people how to spot tornadoes, funnel clouds, wall clouds, and other severe weather phenomena, is offered by the National Weather Service. Used in tandem with Doppler radar information, eyewitness reports can be very helpful for warning the public of an impending tornado, especially when used for ground truthing.
Other spotter groups such as the Amateur Radio Emergency Service, news media, local law enforcement agencies/emergency management organizations, cooperative observers, and the general public also relay information to the National Weather Service for ground truthing.
The NOAA Weather Radio audio of a tornado warning issued for Greensburg, Kansas on May 4, 2007. Greensburg was struck by an EF-5 tornado while the warning was in effect.
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An example of a tornado warning issued in Oklahoma
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000 WFUS54 KOUN 252341 TOROUN OKC017-109-260015- /O.NEW.KOUN.TO.W.0001.150325T2341Z-150326T0015Z/ BULLETIN - EAS ACTIVATION REQUESTED TORNADO WARNING NATIONAL WEATHER SERVICE NORMAN OK 641 PM CDT WED MAR 25 2015 THE NATIONAL WEATHER SERVICE IN NORMAN HAS ISSUED A * TORNADO WARNING FOR... WESTERN OKLAHOMA COUNTY IN CENTRAL OKLAHOMA... SOUTHEASTERN CANADIAN COUNTY IN CENTRAL OKLAHOMA... * UNTIL 715 PM CDT * AT 639 PM CDT...A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO WAS LOCATED OVER MOORE...MOVING EAST AT 40 MPH. HAZARD...TORNADO AND GOLF BALL 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... TINKER AIR FORCE BASE AROUND 645 PM CDT. OTHER LOCATIONS IMPACTED BY THIS TORNADIC THUNDERSTORM INCLUDE WILL ROGERS AIRPORT...THE FAIRGROUNDS...SMITH VILLAGE...THE CAPITOL...LAKE ALUMA...WOODLAWN PARK...WILEY POST AIRPORT AND FOREST PARK. PRECAUTIONARY/PREPAREDNESS ACTIONS... THIS TORNADO WARNING REPLACES THE SEVERE THUNDERSTORM WARNING ISSUED FOR THE SAME AREA. && LAT...LON 3538 9731 3538 9767 3537 9767 3537 9778 3544 9785 3561 9774 3567 9733 TIME...MOT...LOC 2339Z 279DEG 34KT 3534 9750 TORNADO...RADAR INDICATED HAIL...1.75IN $$ MBS
Below is an example of an Environment Canada issued tornado warning for southeastern Saskatchewan.
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 LARGE 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.
- Severe weather terminology (United States)
- Emergency Broadcast System
- Emergency Alert System
- Emergency Communication System
- Tornado Tornado Safety Facts - Tornado Safety 101
- Edwards, Roger. "The Online Tornado FAQ". Storm Prediction Center. Retrieved 6 July 2009.
- "Tulsa TV Weather". Tulsatvmemories.com. Retrieved 2012-02-11.
- "'CATASTROPHIC': Experimental Tornado Warnings to be Explicit". AccuWeather. 2012-04-05. Retrieved 2014-03-12.
- "Tornado Warning". NOAA National Weather Service Glossary. Retrieved 2010-01-10.
- Howerton, Paul (2008-06-12). "Tornado Warning". Iowa Environmental Mesonet NWS Product Archive. Retrieved 2010-01-10.
- NOAA Warning Decision Training Branch (2008-02-26). "Why Storm-Based Warnings?". Storm-Based Warnings. Retrieved 2010-01-11.
- Environment Canada. "Tornado warning". Prairie and Northern Region Weather Watch and Weather Warning Criteria. Retrieved 2010-01-10.
- NWS Office of Climate, Water, and Weather Services. "NWS Dissemination Services". Office of Climate, Water, and Weather Services. Retrieved 2010-01-10.
- National Weather Service Twin Cities, MN (2010-04-22). "Severe Weather Awareness Week". National Oceanic and Atmospheric Administration. Retrieved 2010-12-15.
- Matt Cutt's Alerts Tornado Warnings Infographic -- Retrieved 2013, July 18th - Tornado Warning
- "SKYWARN". Retrieved 2011-01-13.
- Wood, Andy (2008-11-10). "Spotter Report Data Quality". Warning Decision Training Branch. p. 3. Retrieved 2010-01-10.
- Wood, Andy (2008-11-10). "Spotter Report Data Quality". Warning Decision Training Branch. p. 4. Retrieved 2010-01-10.
- "Valid Time Extent Code (VTEC) App". NWSChat. National Weather Service. Retrieved 16 May 2015.