Editing Tornado (section)

===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>