A tornado warning (SAME code: TOR) is an alert issued by national weather forecasting agencies to warn the public that severe thunderstorms with tornadoes are imminent or occurring. 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 (because sirens are not intended to be heard indoors, residents should not completely depend on them. Have more than one way to receive alerts). 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 first such forecast came after the events that transpired 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 Sarg. 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.
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.
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 of 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.
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, before 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 two years later, directing Finley to instead reference "severe local storms", a move motivated by concerns by businessmen in the Great Plains that Finley's forecasts would hurt economic development if potential investors believed their areas were tornado-prone. This position on tornado forecasting would be shared with the U.S. Weather Bureau after it was formation in 1890, fearing that it would incite panic among the public if tornadoes were predicted to occur; the side effect of this 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 that exceeded well over 100.
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 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).
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.
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.
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.
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 has been 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 area and immediate surrounding locations – if not from the relatively narrow tornado itself, from the severe thunderstorm producing (or likely to produce) it. Those 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 in the United States 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 (in the United States, winds exceeding 58 miles per hour (93 km/h) and hail larger than 1 inch (2.5 cm) are the respective defined criteria to classify such phenomena as severe; the criteria varies in other countries) 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 polygonal 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 by the specified sections of the affected jurisdictions), 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. Prior to October 2007, warnings were issued by the National Weather Service on a per-county basis. 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 branch of Environment Canada in Vancouver, Edmonton, Winnipeg, Toronto, Montreal and Halifax (in the province of Ontario, Emergency Management Ontario recently[when?] 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 the Advance Weather Interactive Processing System (AWIPS) and 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 (the actual areas where sirens are activated may vary depending on the relay structure of a given jurisdiction's siren network, with some municipalities activating all sirens within their network even in areas not referenced as being included in the warning). 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 automated phone calls may be made to residents for the same purpose in some areas should such disruptions occur. Additionally, if it is deemed necessary, the National Weather Service has the option of requesting activation of the Emergency Alert System to interrupt television and radio broadcasts to get the bulletin out quickly.
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[update] (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.
The SKYWARN program, which trains citizens on 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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Below is an example of a Tornado Warning issued by the National Weather Service office in Norman, Oklahoma, using the new experimental Impact Based Warning (IBW) format.
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
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