Wall cloud
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Wall cloud (Murus) | |
---|---|
Abbreviation | Cb mur. |
Symbol | |
Genus | Cumulonimbus (heap, rain) |
Species |
|
Snow pellets or Hail , heavy at times |
A wall cloud (murus
Genesis
Wall clouds are formed by a process known as
Structure
Wall clouds can be anywhere from a fraction of 1 mi (1.6 km) wide to over 5 mi (8 km) across. Wall clouds form in the inflow region, on the side of the storm coinciding with the direction of the steering winds (deep layer winds through the height of the storm). In the Northern Hemisphere wall clouds typically form at the south or southwest end of a supercell. This is in the rear of the supercell near the main updraft and most supercells move in a direction with northeasterly components, for supercells forming in northwest flow situations and moving southeastward, the wall cloud may be found on the northwest or back side of such storms. Rotating wall clouds are visual evidence of a mesocyclone.
Associated features
Some wall clouds have a feature similar to an "eye", as in a
Attached to many wall clouds, especially in moist environments, is a cauda
Some wall clouds also have a band of cloud fragments encircling the top of the wall cloud where it meets the ambient cloud base; this feature is a collar cloud.[7]
Another accessory cloud is the flumen,[1] commonly known as the beaver's tail. It is formed by the warm, humid inflow of a strong thunderstorm, and is often mistaken for tornadoes. Although the presence of a flumen is associated with tornado risk, the flumen, similar to scud clouds, does not rotate.
Wall cloud vs. shelf cloud
Many storms contain
Shelf clouds most often appear on the leading edge of a thunderstorm as they are formed by condensation from the cool outflow of the storm that lifts warmer air in the ambient environment (at the
Supercell and tornado significance
The wall cloud feature was first identified by
Tornadogenesis is most likely when the wall cloud is persistent with rapid ascent and rotation. The wall cloud typically precedes tornadogenesis by ten to twenty minutes but may be as little as one minute or more than an hour. Often, the degree of ascent and rotation increase markedly shortly before tornadogenesis, and sometimes the wall cloud will descend and "bulk" or "tighten". Tornadic wall clouds tend to have strong, persistent, and warm inflow air. This should be sensible at the surface if one is in the inflow region; in the Northern Hemisphere, this is typically to the south and southeast of the wall cloud. Large tornadoes tend to come from larger, lower-wall clouds closer to the back of the rain curtain (providing less visual warning time to those in the path of an organized storm).
Although it is rotating wall clouds that contain most
Usually, but not always, the dry slot occlusion is visible (assuming one's line of sight is not blocked by precipitation) throughout the tornado life cycle. The wall cloud withers and will often be gone by the time the tornado dissipates. If conditions are favorable, then, often even before the original tornado lifts, another wall cloud and occasionally a new tornado may form downwind of the old wall cloud, typically to the east or the southeast in the Northern Hemisphere (east or northeast in the Southern Hemisphere). This process is known as cyclic tornadogenesis and the resulting series of tornadoes as a tornado family.
The rotation of wall clouds is usually cyclonic; anticyclonic wall clouds may occur with anti-mesocyclones or with mesovortices on the leading edge of a QLCS (Again, this relationship is reversed in the Southern Hemisphere).[11]
Other usages of the term
The dense cumulonimbus cloud cover of the
See also
References
- ^ a b c Sutherland, Scott (March 23, 2017). "Cloud Atlas leaps into 21st century with 12 new cloud types". The Weather Network. Pelmorex Media. Retrieved 24 March 2017.
- ^ "Definition of Wall Cloud". A Comprehensive Glossary of Weather. Retrieved 2013-01-21.
- OCLC 39732655.
- OCLC 39732655.
- ^ a b c Chance Hayes, National Weather Service Wichita, Kansas. "Storm Fury on the Plains." Storm Spotter Training. 4H Building, Salina, Kansas. 22 Feb. 2010. Lecture.
- ^ a b Fujita, T. (1959). "A detailed analysis of the Fargo tornadoes of June 20, 1957,". U.S. Wea. Bur. Res. Paper 42: 15.
- OCLC 39732655.
- ^ Drummond, David. "Advanced Module". Skywarn Storm Spotter Guides. Archived from the original on 2004-01-11. Retrieved 2014-06-01.
- ^ "The Tornado". Thunderstorms and Severe Weather. the University of Texas. 29 Jun 1998. Retrieved 2014-06-01.
- .
- ISBN 9780534372149.
- ^ "Glossary of NHC Terms". National Hurricane Center. Retrieved 2014-06-01.
- Wall clouds (University of Illinois)
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External links
- "Wall cloud". Glossary of Meteorology. AMS.