Tornado warning - AbsoluteAstronomy.com

A tornado warning is an alert issued by government weather services to warn that severe thunderstorms

Thunderstorm

A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...

with tornadoes

Tornado

A tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider...

may be imminent. It can be issued after a tornado or funnel cloud

Funnel cloud

A funnel cloud is a funnel-shaped cloud of condensed water droplets, associated with a rotating column of wind and extending from the base of a cloud but not reaching the ground or a water surface. A funnel cloud is usually visible as a cone-shaped or needle like protuberance from the main cloud...

has been spotted by eye, or more commonly if there are radar

Weather radar

Weather radar, also called weather surveillance radar and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, estimate its type . Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the...

indications of tornado formation. When this happens, the tornado siren

Civil defense siren

A civil defense siren is a mechanical or electronic device for generating sound to...

s may sound in that area, letting people know that a tornado was seen or is forming nearby. Issuance of a tornado warning indicates that residents should take immediate safety precautions. It is a higher level of alert than a tornado watch

Tornado watch

A tornado watch is issued when conditions are right for a tornado to form. Since any thunderstorm capable of producing a tornado is defined as severe, a tornado watch is also automatically a severe thunderstorm watch...

, but it can be surpassed by an even higher alert known as a tornado emergency

Tornado emergency

A Tornado Emergency is enhanced wording of tornado warnings used by the National Weather Service in the United States during significant tornado occurrences in highly populated areas...

Early history

The first official tornado forecast (and tornado warning) was made by United States Air Force

United States Air Force

The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...

Capt. (later Col.) Robert C. Miller

Robert C. Miller

Col. Robert C. Miller, USAF , was an American meteorologist, who pioneered severe convective storms forecasting and applied research, developing an empirical forecasting method, identifying many features associated with severe thunderstorms, a forecast checklist and manuals, and is known for the...

and Major Ernest Fawbush, on March 25, 1948. The USAF pioneered tornado forecasting and tornado warnings, mainly due to the 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 they predicted tornadoes. In 1950, the Weather Bureau revoked their ban on the word "tornado", thus allowing public tornado warnings.

Despite the U.S. Weather Bureau's lifting of their ban on tornado warnings, the Federal Communications Commission

Federal Communications Commission

The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...

continued to bar television and radio from broadcasting tornado warnings on-air due to possibly inciting panic in the public. Broadcast media did not follow until 1954, when meteorologist Harry Volkman

Harry Volkman

Harry Volkman is a popular former meteorologist from Oklahoma and later Chicago, Illinois. He is known for being the first weatherman to issue a tornado warning....

broadcast the first televised tornado warning over WKY-TV (now KFOR-TV

KFOR-TV

KFOR-TV, virtual channel 4 , is the NBC-affiliated television station in Oklahoma City, Oklahoma. KFOR-TV is owned by Local TV, a subsidiary of the private equity group Oak Hill Capital Partners, in a duopoly with MyNetworkTV affiliate KAUT-TV ; its studios are located at 444 East Britton Road in...

) in Oklahoma City, due to his belief that the banning of tornado warnings over broadcast media cost lives; the FCC eventually lifted their ban on broadcasting tornado warnings.

Tornado Alert

For many years up 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, &c. for another decade or so.

The kinds of situations 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

Wall cloud

A wall cloud is a large, lowering, and rotating base of a cumulonimbus cloud that potentially forms tornadoes. It is typically beneath the rain-free base portion of a deep cumulus cloud , and indicates the area of primary and strongest updraft which condenses into cloud at altitudes lower than...

has formed, and so on. 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

Pulse-doppler radar

Pulse-Doppler is a 4D radar system capable of detecting both target 3D location as well as measuring radial velocity . It uses the Doppler effect to avoid overloading computers and operators as well as to reduce power consumption...

weather radar

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 officially issued was discussed in earnest following the 3–4 April 1974 Super Outbreak

Super Outbreak

The Super Outbreak is the second largest tornado outbreak on record for a single 24-hour period, just behind the tornado outbreak of April 25–28, 2011...

Criteria

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
Weather radar
Weather radar, also called weather surveillance radar and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, estimate its type . Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the...

, or
a waterspout
Waterspout
A waterspout is an intense columnar vortex that occurs over a body of water and is connected to a cumuliform cloud. In the common form, it is a non-supercell tornado over water. While it is often weaker than most of its land counterparts, stronger versions spawned by mesocyclones do occur...

is headed for landfall
Landfall (meteorology)
Landfall is the event of a tropical cyclone or a waterspout coming onto land after being over water. When a waterspout makes landfall it is reclassified as a tornado, which can then cause damage inland...

.

A tornado warning means there is immediate danger for the warned and immediately surrounding area—if not from the relatively narrow tornado

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 should not be confused with a tornado watch

Tornado watch

(issued by a national guidance center, the Storm Prediction Center

Storm Prediction Center

The Storm Prediction Center , located in Norman, Oklahoma, is tasked with forecasting the risk of severe thunderstorms and tornadoes in the contiguous United States. The agency issues convective outlooks, mesoscale discussions, and watches as a part of this process...

) 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

Downburst

A downburst is created by an area of significantly rain-cooled air that, after reaching ground level, spreads out in all directions producing strong winds. Unlike winds in a tornado, winds in a downburst are directed outwards from the point where it hits land or water...

and/or large hail

Hail

Hail is a form of solid precipitation. It consists of balls or irregular lumps of ice, each of which is referred to as a hail stone. Hail stones on Earth consist mostly of water ice and measure between and in diameter, with the larger stones coming from severe thunderstorms...

from the thunderstorm. A severe thunderstorm warning

Severe thunderstorm warning

A severe thunderstorm warning is issued when trained storm spotters or a Doppler weather radar indicate a strong thunderstorm is producing dangerously large hail or high winds, capable of causing significant damage. In the United States, it does not account for lightning or flooding...

can be upgraded suddenly to a tornado warning should conditions warrant.

In the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, local offices of the National Weather Service

National Weather Service

The National Weather Service , once known as the Weather Bureau, is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration of the United States government...

issue warnings for tornadoes and severe thunderstorms based on the path of a storm, although entire counties are sometimes included, especially if they are small. Warnings were issued on a per-county basis before October 2007.

In Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, similar criteria are used and warnings are issued by regional offices of the Meteorological Service of Canada

Meteorological Service of Canada

The Meteorological Service of Canada , also known as "The Canadian Weather Service", is a division of Environment Canada, which primarily provides public meteorological information and weather forecasts and warnings of severe weather and other environmental hazards...

of Environment Canada

Environment Canada

Environment Canada , legally incorporated as the Department of the Environment under the Department of the Environment Act Environment Canada (EC) (French: Environnement Canada), legally incorporated as the Department of the Environment under the Department of the Environment Act Environment...

in Vancouver

Vancouver

Vancouver is a coastal seaport city on the mainland of British Columbia, Canada. It is the hub of Greater Vancouver, which, with over 2.3 million residents, is the third most populous metropolitan area in the country,...

, Edmonton

Edmonton

Edmonton is the capital of the Canadian province of Alberta and is the province's second-largest city. Edmonton is located on the North Saskatchewan River and is the centre of the Edmonton Capital Region, which is surrounded by the central region of the province.The city and its census...

, Winnipeg

Winnipeg

Winnipeg is the capital and largest city of Manitoba, Canada, and is the primary municipality of the Winnipeg Capital Region, with more than half of Manitoba's population. It is located near the longitudinal centre of North America, at the confluence of the Red and Assiniboine Rivers .The name...

, Toronto

Toronto

Toronto is the provincial capital of Ontario and the largest city in Canada. It is located in Southern Ontario on the northwestern shore of Lake Ontario. A relatively modern city, Toronto's history dates back to the late-18th century, when its land was first purchased by the British monarchy from...

, Montreal

Montreal

Montreal is a city in Canada. It is the largest city in the province of Quebec, the second-largest city in Canada and the seventh largest in North America...

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 siren

Civil defense siren

A civil defense siren is a mechanical or electronic device for generating sound to...

s 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.

Ground truthing

The SKYWARN

Skywarn

SKYWARN is a program of the United States' National Weather Service . Its mission is to collect reports of localized severe weather. These reports are used to aid forecasters in issuing and verifying severe weather watches and warnings and to improve the forecasting and warning processes and the...

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 truth

Ground truth

Ground truth is a term used in cartography, meteorology, analysis of aerial photographs, satellite imagery and a range of other remote sensing techniques in which data are gathered at a distance. Ground truth refers to information that is collected "on location." In remote sensing, this is...

ing.

Other spotter groups such as the Amateur Radio Emergency Service

Amateur Radio Emergency Service

In the United States and Canada, the Amateur Radio Emergency Service is a corps of trained amateur radio operator volunteers organized to assist in public service and emergency communications...

, news media, local law enforcement agencies/emergency management

Emergency management

Emergency management is the generic name of an interdisciplinary field dealing with the strategic organizational management processes used to protect critical assets of an organization from hazard risks that can cause events like disasters or catastrophes and to ensure the continuance of the...

organizations, cooperative observers, and the general public also relay information to the National Weather Service for ground truthing.

Tornado Emergency

When a large, extremely violent tornado is about to impact a densely populated area, the Weather Service has the option of issuing a severe weather statement with unofficial, enhanced wording; this is called a tornado emergency

Tornado emergency

A Tornado Emergency is enhanced wording of tornado warnings used by the National Weather Service in the United States during significant tornado occurrences in highly populated areas...

. This category of weather statement is the highest and most urgent level relating to tornadoes, albeit unofficially. In some cases, a Tornado Emergency has been declared in the initial issuance of the Tornado Warning.

The levels of severity increase as follows:

Convective Outlook mentioning tornado potential
Public Severe Weather Outlook mentioning tornado potential
Tornado Watch
Tornado watch
A tornado watch is issued when conditions are right for a tornado to form. Since any thunderstorm capable of producing a tornado is defined as severe, a tornado watch is also automatically a severe thunderstorm watch...
Particularly Dangerous Situation
Particularly dangerous situation
A particularly dangerous situation is a type of enhanced wording first used by the National Weather Service's Storm Prediction Center in Norman, Oklahoma on certain severe weather watches...

Tornado Watch
Tornado Warning
Tornado Emergency
Tornado emergency
A Tornado Emergency is enhanced wording of tornado warnings used by the National Weather Service in the United States during significant tornado occurrences in highly populated areas...

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, etc.

Examples



BULLETIN - EAS ACTIVATION REQUESTED

TORNADO WARNING

NATIONAL WEATHER SERVICE NORMAN OK

533 PM CDT TUE MAY 24 2011



THE NATIONAL WEATHER SERVICE IN NORMAN HAS ISSUED A



 TORNADO WARNING FOR...


  CENTRAL LOGAN COUNTY IN CENTRAL OKLAHOMA...

  PAYNE COUNTY IN CENTRAL OKLAHOMA...

  SOUTHEASTERN NOBLE COUNTY IN NORTHERN OKLAHOMA...



 UNTIL 630 PM CDT




 AT 533 PM CDT...A LARGE... VIOLENT TORNADO WAS LOCATED NEAR


  GUTHRIE...MOVING NORTHEAST AT 35 MPH.



 LOCATIONS IN THE WARNING INCLUDE COYLE...GLENCOE...GUTHRIE...


  INGALLS...LAKE CARL BLACKWELL...LAKE MCMURTRY...LANGSTON...

  MORRISON...PERKINS...QUAY...RIPLEY...SOONER LAKE...STILLWATER AND

  YALE.



THIS INCLUDES INTERSTATE 35 BETWEEN MILE MARKERS 157 AND 175.



PRECAUTIONARY/PREPAREDNESS ACTIONS...



THIS IS AN EXTREMELY DANGEROUS AND LIFE THREATENING SITUATION. IF YOU

ARE IN THE PATH OF THIS LARGE AND DESTRUCTIVE TORNADO... TAKE COVER

IMMEDIATELY. A BASEMENT OR STORM SHELTER IS BEST. OTHERWISE...TAKE

COVER IN AN INTERIOR CLOSET OR BATHROOM AWAY FROM OUTSIDE WALLS AND

WINDOWS. COVER YOUR HEAD WITH PILLOWS AND BLANKETS.



&&



LAT...LON 3635 9702 3635 9695 3633 9691 3626 9691

      3626 9683 3624 9681 3617 9681 3618 9663

      3617 9661 3610 9662 3585 9740 3594 9751

      3646 9703

TIME...MOT...LOC 2233Z 235DEG 30KT 3591 9741



$$

What to do when a Tornado Warning is issued

When a Tornado Warning is issued, people should try to move to the lowest level of their house or into the basement; if there is no basement, move to an interior room (such as a closet or bathroom) and try to have as many walls as possible between you and the outside.
If able, people should cover themselves with blankets or pillows to protect from flying glass or other debris that could be in the air.
If in a mobile home, people should evacuate it immediately for sturdy shelter. If no shelter is available, lie flat in a ditch or other low spot. People should cover their heads with their hands. Some mobile homes have become airborne, or tumbled down hillsides.
If driving, people should not seek shelter under an overpass. Instead, they should get out of the vehicle and lie flat in a ditch or other low spot.
The National Weather Service suggests people should not go outside, should stay away from windows, protect themselves from flying debris, and postpone travel until the storms have passed.
It is also suggested that residents and businesses have a NOAA weather radio. Civil defense siren
Civil defense siren
A civil defense siren is a mechanical or electronic device for generating sound to...

s are intended for outdoor warning only.