Editing Tornado (section)

==Detection==
[[File:Tornado1857.jpg|thumb|right|Path of a tornado across Wisconsin on August 21, 1857]]
{{Main|Convective storm detection}}
Rigorous attempts to warn of tornadoes began in the United States in the mid-20th century. Before the 1950s, the only method of detecting a tornado was by someone seeing it on the ground. Often, news of a tornado would reach a local weather office after the storm. However, with the advent of weather radar, areas near a local office could get advance warning of severe weather. The first public [[tornado warning]]s were issued in 1950 and the first [[tornado watch]]es and [[convective outlooks]] came about in 1952. In 1953, it was confirmed that [[hook echo]]es were associated with tornadoes.<ref>{{cite web|year=2008|title=The First Tornadic Hook Echo Weather Radar Observations|publisher=Colorado State University|url=http://www.chill.colostate.edu/w/CHILL_history#The_First_Tornadic_Hook_Echo_Weather_Radar_Observations|access-date=2008-01-30|archive-date=2008-08-20|archive-url=https://web.archive.org/web/20080820093538/http://www.chill.colostate.edu/w/CHILL_history#The_First_Tornadic_Hook_Echo_Weather_Radar_Observations|url-status=live}}</ref> By recognizing these radar signatures, meteorologists could detect thunderstorms probably producing tornadoes from several miles away.<ref name="hook echoes">{{cite journal|first=Paul M.|last=Markowski|author-link=Paul Markowski|title=Hook Echoes and Rear-Flank Downdrafts: A Review|journal=Mon. Wea. Rev.|volume=130 |issue=4|pages=852–76|doi=10.1175/1520-0493(2002)130<0852:HEARFD>2.0.CO;2|date=April 2002|bibcode = 2002MWRv..130..852M |s2cid=54785955 |doi-access=free}}</ref>

=== Radar ===
{{See also|Pulse-Doppler radar|weather radar}}
[[File:NapervilleWoodridgeRadarGraphic.png|thumb|right|[[2021 Naperville–Woodridge tornado|A 2021 EF3 tornado in Illinois]] is displayed across various [[NEXRAD]] data types. [[Weather radar#Polarization|Dual-polarization]] and [[Weather radar#Velocity|Doppler velocity]] products have greatly improved forecasters' ability to detect tornadoes while they are ongoing or imminent when no visual confirmation is available.]]
Today most developed countries have a network of weather radars, which serves as the primary method of detecting hook signatures that are likely associated with tornadoes. In the United States and a few other countries, Doppler weather radar stations are used. These devices measure the velocity and radial [[direction (geometry, geography)|direction]] (towards or away from the radar) of the winds within a storm, and so can spot evidence of rotation in storms from over {{convert|100|mi|km|abbr=in|order=flip}} away. When storms are distant from a radar, only areas high within the storm are observed and the important areas below are not sampled.<ref name="airbusradar">{{cite web|url=http://www.skybrary.aero/bookshelf/books/163.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.skybrary.aero/bookshelf/books/163.pdf |archive-date=2022-10-09 |url-status=live|title=Flight Briefing Notes: Adverse Weather Operations Optimum Use of Weather Radar|page=2|author=Airbus|publisher=SKYbrary|date=2007-03-14|access-date=2009-11-19 |author-link=Airbus}}</ref> Data resolution also decreases with distance from the radar. Some meteorological situations leading to tornadogenesis are not readily detectable by radar and tornado development may occasionally take place more quickly than radar can complete a scan and send the batch of data. [[Weather radar#Velocity|Doppler weather radar]] systems can detect [[mesocyclone]]s within a supercell thunderstorm. This allows meteorologists to predict tornado formations throughout thunderstorms.<ref>{{Cite web|url=http://www.nssl.noaa.gov/tools/radar/|title=Research tools: Radar|website=www.nssl.noaa.gov|publisher=NOAA National Severe Storms Laboratory|access-date=October 14, 2016|archive-url=https://web.archive.org/web/20161014053017/http://www.nssl.noaa.gov/tools/radar/|archive-date=2016-10-14|url-status=dead}}</ref>

===Storm spotting===
{{citation needed span|In the mid-1970s, the U.S. [[National Weather Service]] (NWS) increased its efforts to train [[Storm spotting|storm spotters]] so they could spot key features of storms that indicate severe hail, damaging winds, and tornadoes, as well as storm damage and [[flash flood]]ing. The program was called [[Skywarn]], and the spotters were local sheriff's deputies, state troopers, firefighters, ambulance drivers, [[amateur radio operator]]s, [[civil defense]] (now [[emergency management]]) spotters, [[storm chasing|storm chasers]], and ordinary citizens. When severe weather is anticipated, local weather service offices request these spotters to look out for severe weather and report any tornadoes immediately, so that the office can warn of the hazard.|date=December 2021}}

Spotters usually are trained by the NWS on behalf of their respective organizations, and report to them. The organizations activate public warning systems such as [[Civil defense siren|sirens]] and the [[Emergency Alert System]] (EAS), and they forward the report to the NWS.<ref name="spotter history">{{cite journal|first1=Charles A. III|last1=Doswell|first2=Alan R.|last2=Moller|first3=Harold E.|last3=Brooks|title=Storm Spotting and Public Awareness since the First Tornado Forecasts of 1948|journal=Weather Forecast.|volume=14|issue=4|pages=544–57|year=1999|doi=10.1175/1520-0434(1999)014<0544:SSAPAS>2.0.CO;2|bibcode = 1999WtFor..14..544D|url=http://www.flame.org/~cdoswell/publications/stormspotting_99.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.flame.org/~cdoswell/publications/stormspotting_99.pdf |archive-date=2022-10-09 |url-status=live|citeseerx=10.1.1.583.5732}}</ref>
There are more than 230,000 trained Skywarn weather spotters across the United States.<ref name="NWS SKYWARN">{{cite web|url=http://www.weather.gov/skywarn/|date=2009-02-06|author=National Weather Service|publisher=National Oceanic and Atmospheric Administration|title=What is SKYWARN?|access-date=2009-12-13|author-link=National Weather Service|archive-date=2009-12-10|archive-url=https://web.archive.org/web/20091210075145/http://www.weather.gov/skywarn/|url-status=live}}</ref>

In Canada, a similar network of volunteer weather watchers, called [[Canwarn]], helps spot severe weather, with more than 1,000 volunteers.<ref name="environment Canada detection">{{cite web|url=http://www.mb.ec.gc.ca/air/summersevere/ae00s10.en.html |title=Tornado Detection at Environment Canada |access-date=2009-12-13 |publisher=Environment Canada |date=2004-06-02 |url-status=dead |archive-url=https://web.archive.org/web/20100407123441/http://www.mb.ec.gc.ca/air/summersevere/ae00s10.en.html |archive-date=2010-04-07 }}</ref> In Europe, several nations are organizing spotter networks under the auspices of [[Skywarn Europe]]<ref>{{cite web|date=2009-05-31 |url=http://www.skywarn.eu/ |title=Skywarn Europe |author=European Union |access-date=2009-12-13 |author-link=European Union |url-status=dead |archive-url=https://web.archive.org/web/20090917011719/http://www.skywarn.eu/ |archive-date=2009-09-17 }}</ref> and the Tornado and Storm Research Organisation (TORRO) has maintained a network of spotters in the United Kingdom since 1974.<ref>{{cite web|url=http://www.torro.org.uk/site/history.php|title=A Brief History|first=Terence|last=Meaden|year=1985|publisher=Tornado and Storm Research Organisation|access-date=2009-12-13|archive-date=2015-06-26|archive-url=https://web.archive.org/web/20150626221845/http://www.torro.org.uk/site/history.php|url-status=dead}}</ref>

Storm spotters are required because radar systems such as [[NEXRAD]]  detect signatures that suggest the presence of tornadoes, rather than tornadoes as such.<ref name="NSSLsearch">{{cite web|url=http://www.nssl.noaa.gov/primer/tornado/tor_detecting.html|title=Detecting Tornadoes: What Does a Tornado Look Like?|author=National Severe Storms Laboratory|publisher=National Oceanic and Atmospheric Administration|date=2006-11-15|access-date=2009-12-13|author-link=National Severe Storms Laboratory|archive-url=https://web.archive.org/web/20120523170026/http://www.nssl.noaa.gov/primer/tornado/tor_detecting.html|archive-date=2012-05-23|url-status=dead}}</ref> Radar may give a warning before there is any visual evidence of a tornado or an imminent one, but [[ground truth]] from an observer can give definitive information.<ref>{{cite web|url=http://www.stormeyes.org/tornado/verf/|title=Proposals For Changes in Severe Local Storm Warnings, Warning Criteria and Verification|year=2003|access-date=2009-12-13|first1=Roger|last1=Edwards|first2=Elke|last2=Edwards|archive-date=2009-06-28|archive-url=https://web.archive.org/web/20090628132309/http://www.stormeyes.org/tornado/verf/|url-status=live}}</ref> The spotter's ability to see what radar cannot is especially important as distance from the radar site increases, because the radar beam becomes progressively higher in altitude further away from the radar, chiefly due to curvature of Earth, and the beam also spreads out.<ref name="airbusradar"/>

===Visual evidence===
[[File:Wall cloud12 - NOAA.jpg|thumb|right|A rotating [[wall cloud]] with [[rear flank downdraft]] clear slot evident to its left rear]]
Storm spotters are trained to discern whether or not a storm seen from a distance is a supercell. They typically look to its rear, the main region of [[updraft]] and inflow. Under that updraft is a rain-free base, and the next step of [[tornadogenesis]] is the formation of a rotating [[wall cloud]]. The vast majority of intense tornadoes occur with a wall cloud on the backside of a supercell.<ref name="Basic Spotter Guide"/>

Evidence of a supercell is based on the storm's shape and structure, and cloud tower features such as a hard and vigorous updraft tower, a persistent, large [[overshooting top]], a hard anvil (especially when backsheared against strong upper level [[wind]]s), and a corkscrew look or [[striation (meteorology)|striations]]. Under the storm and closer to where most tornadoes are found, evidence of a supercell and the likelihood of a tornado includes inflow bands (particularly when curved) such as a "beaver tail", and other clues such as strength of inflow, warmth and moistness of inflow air, how outflow- or inflow-dominant a storm appears, and how far is the front flank precipitation core from the wall cloud. Tornadogenesis is most likely at the interface of the updraft and [[rear flank downdraft]], and requires a balance between the outflow and inflow.<ref name="Advanced Spotter Guide">{{cite web|url=http://www.crh.noaa.gov/oax/skywarn/adv_spotters.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.crh.noaa.gov/oax/skywarn/adv_spotters.pdf |archive-date=2022-10-09 |url-status=live|title=Advanced Spotters' Field Guide|publisher=National Oceanic and Atmospheric Administration|access-date=2009-12-13|date=2003-01-03}}</ref>

Only wall clouds that rotate spawn tornadoes, and they usually precede the tornado between five and thirty minutes. Rotating wall clouds may be a visual manifestation of a low-level mesocyclone. Barring a low-level boundary, tornadogenesis is highly unlikely unless a rear flank downdraft occurs, which is usually visibly evidenced by evaporation of cloud adjacent to a corner of a wall cloud. A tornado often occurs as this happens or shortly afterwards; first, a funnel cloud dips and in nearly all cases by the time it reaches halfway down, a surface swirl has already developed, signifying a tornado is on the ground before condensation connects the surface circulation to the storm. Tornadoes may also develop without wall clouds, under flanking lines and on the leading edge. Spotters watch all areas of a storm, and the [[cloud base]] and surface.<ref name="NSSL tornadoes">{{cite web|title=Questions and Answers about Tornadoes|work=A Severe Weather Primer|publisher=National Severe Storms Laboratory|date=2006-11-15|url=http://www.nssl.noaa.gov/primer/tornado/tor_basics.html|access-date=2007-07-05|archive-url=https://web.archive.org/web/20120809070939/http://www.nssl.noaa.gov/primer/tornado/tor_basics.html|archive-date=2012-08-09|url-status=dead}}</ref>