Tornadoes that spin in the opposite direction of normal tornadoes
An anticyclonic tornado is a tornado which rotates in a clockwise direction in the Northern Hemisphere and a counterclockwise direction in the Southern Hemisphere.[1] The term is a naming convention denoting the anomaly from normal rotation which is cyclonic in upwards of 98 percent of tornadoes.[citation needed] Many anticyclonic tornadoes are smaller and weaker than cyclonic tornadoes, forming from a different process, as either companion/satellite tornadoes or nonmesocyclonic tornadoes.[2]
Most strong tornadoes form in the inflow and updraft area bordering the updraft-downdraft interface (which is also near the mesoscale "triple point") zone of supercellthunderstorms. The thunderstorm itself is rotating, with a rotating updraft known as a mesocyclone, and then a smaller area of rotation at lower altitude the tornadocyclone (or low-level mesocyclone) which produces or enables the smaller rotation that is a tornado. All of these may be quasi-vertically aligned continuing from the ground to the mid-upper levels of the storm. All of these cyclones and scaling all the way up to large extratropical (low-pressure systems) and tropical cyclones rotate cyclonically. Rotation in these synoptic scale systems stems partly from the Coriolis effect, but thunderstorms and tornadoes are too small to be significantly affected. The common property here is an area of lower pressure, thus surrounding air flows into the area of less dense air forming cyclonic rotation. The rotation of the thunderstorm itself is induced mostly by vertical wind shear, specifically clockwise turning as altitude increases (called a veered vertical profile, although backed profiles can occur with anticyclonic supercells).
Various processes can produce an anticyclonic tornado. Most often they are satellite tornadoes of larger tornadoes which are directly associated with the tornadocyclone and mesocyclone. Occasionally anticyclonic tornadoes occur as an anticyclonic companion (mesoanticyclone) to a mesocyclone within a single storm. Anticyclonic tornadoes can occur as the primary tornado with a mesocyclone and under a rotating wall cloud. Also, anticyclonic supercells (with mesoanticyclone), which usually are storms that split and move to the left of the parent storm motion, though very rarely spawning tornadoes, spawn anticyclonic tornadoes. There is an increased incidence of anticyclonic tornadoes associated with tropical cyclones, and mesovortices within bow echoes may spawn anticyclonic tornadoes.[3]
The first anticyclonic tornado associated with a mesoanticyclone was spotted on WSR-88D weather radar in Sunnyvale, California on May 4, 1998. The tornado was an F2 on the Fujita Scale.[4]
First known tornado filmed in the US, a companion or cyclic tornado to another significant tornado. It is officially listed as one tornado event by the CDNS report and the NCDC.[5][6]
Law enforcement reported a landspout tornado north and east of the Maxwell Interstate 80 interchange. The tornado touched down briefly in an open area. Based on radar.[24]
Tornado outbreak of May 10–13, 2010 – Third of five anticyclonic tornadoes on this day; it was likely a satellite tornado to the Norman–Little Axe, Oklahoma EF4 tornado.[25][28]
Tornado outbreak of May 10–13, 2010 – Fourth of five anticyclonic tornadoes on this day; was up to a 1⁄2 mile (0.80 km) wide and was briefly accompanied by a cyclonic EF0 satellite tornado.[25][29]
Tornadoes of 2016#March 30–April 1 – A brief anticyclonic tornado snapped and uprooted trees, downed several large tree branches and inflicted minor roof damage to a home and barn.[36][37]
"This very brief track was found in Sentinel satellite imagery and stayed in fields for its existence. Based on the location in the supercell, inflow wind trajectories along the left side of the track, and striation patterns in the fields, there is a high likelihood that this was an anti-cyclonic tornado."[46]
A strong anticyclonic tornado that occurred simultaneously with an EF3 tornado to its northwest. Homes were damaged, storage buildings were destroyed, and numerous trees and power poles were snapped.[48]