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Meteorology  Tornadic activity  Tornado alley

Tornado Vortex Signatures in Doppler radial velocity patterns
The most important phenomena associated with severe convection are tornadoes. When a tornado is present, it is usually small enough that it fits within one or two beam widths.

Tornado formation
Tornadoes develop from thunderstorms, most frequently supercell thunderstorms, though they also occur within squall lines and hurricanes. They are believed to be produced when cool air overrides a layer of warm air, forcing the warm air to rise rapidly.

'Tornado alley' claims average 80 lives every year
The plains of the central United States are no strangers to tornadoes. About a thousand occur every year in 'Tornado Alley', killing on average 80 people and leaving a trail of devastation in their wake at a cost of 300 million dollars.

The afternoon of 2 February 1918 was humid and unsettled in Melbourne, with a slow-moving low pressure trough crossing Victoria. As the trough approached, heavy thunderclouds built up. About 4.

Tornado - A violently rotating narrow column of air in contact with the ground and extending from a thunderstorm base. The tornado is most often found in the southwest quadrant of the storm, near the trailing edge of the cumulonimus cloud.

~: A violently rotating column of air, a vortex, formed in a thunderstorm which is in contact with both the parent cloud and the ground with a diameter between tens and hundreds of metres.

~ Family - A series of ~es produced by a single supercell, resulting in damage path segments along the same general line.

~ Watch- A ~ Watch outlines an area where large hail and damaging wind threats, as well as the possibility of multiple ~es are possible.

~es often form in the hot, humid weather of a late spring or summer afternoon. The thunderstorms that produce ~es frequently develop in the warm, moist air near the fronts or transition zones between warm and cold air masses.

A funnel-shaped whirlwind which extends to the ground from storm clouds
Tropics ...

~: A violent rotating column of air, in contact with the ground, pendant from a cumulonimbus cloud. A ~ does not require the visible presence of a funnel cloud. It has a typical width of tens to hundreds of meters and a lifespan of minutes to hours.

~ Vortex Signature
An image of a ~ on the Doppler radar screen that shows up as a small region of rapidly changing wind speeds inside a mesocyclone.

A violently rotating column of air that extends downward from a cumulonimbus cloud and moves in a narrow path along the ground.
Tropics (Tropical Climate) ...

~- a violent, rotating column of air extending from the ground to a thunderstorm.
Trade Winds- easterly-blowing winds that are found on either side of the equator and blow northeasterly in the Northern Hemisphere and southeasterly in the Southern Hemisphere.

~: small mass of air that spins rapidly about an almost vertical axis and forms a funnel cloud that contacts the ground. Comes down from a cumulonimbus cloud and is considered probably the most destructive of all weather systems.

(Twister) A violently rotating storm of small diameter; the most violent weather phenomenon. It is produced in a very severe thunderstorm and appears as a funnel cloud extending from the base of a Cumulonimbus to the ground.

The cyclone of the temperate regions, the ~ and the hurricane are all vortex-like low-pressure areas, but of very different character. The temperate cyclone is fed by the energy available at fronts between air masses, covers a large area, and has moderate winds.

~ An intense, rotating column of air that protrudes from a cumulonimbus cloud in the shape of a funnel or a rope and touches the ground. (See Funnel cloud.)
Trade winds The winds that occupy most of the tropics and blow from the subtropical highs to the equatorial low.

~ - A violent rotating column of air, usually forming a pendant from a cumulonimbus cloud with the circulation reaching the ground. It nearly always starts as a funnel cloud and may be accompanied by a loud roaring noise.

~ alley Region of maximum ~ frequency in North America; a corridor stretching from central Texas northward into Oklahoma, Kansas and Nebraska, and eastward into central Illinois and Indiana, ...

~ Warning
A warning issued by Environment Canada's Meteorological Service (MSC), when at least one ~ is imminent, as indicated by observations, reports and/or radar scans.
~ Warning (Marine) ...

~ (sometimes called cyclone, twister)—A violently rotating column of air, pendant from a cumulonimbus cloud, and nearly always observable as “funnel-shaped.“ It is the most destructive of all small-scale atmospheric phenomena.

A violently rotating column of air in contact with and extending between a convective cloud and the surface of the earth. It is the most destructive of all storm-scale atmospheric phenomena.

~ A twisting, spinning funnel of low pressure air. The most unpredictable weather event, ~es are created during powerful thunderstorms. As a column of warm air rises, air rushes in at ground level and begins to spin. If the storm gathers energy, a twisting, spinning funnel develops.

~ Alley- The area of the United States in which ~es are most frequent. It encompasses the great lowland areas of the Mississippi, the Ohio, and lower Missouri River Valleys.

~ A rapidly whirling funnel-shaped cloud that reaches down from a storm cloud to touch earth's surface, usually leaving a destructive path
Add Cards ...

~ Watch - Issued when conditions are favorable for the development of severe thunderstorms and possible ~s in and close to a defined area.
Wall Cloud - An area of clouds that extends beneath a severe thunderstorm. If a wall cloud rotates, it might precede ~ development.

TVS- ~ Vortex Signature
TWEAK- To change slightly. Often in reference to slightly changing MOS output or any other form of model guidance.
UA- Upper Air ...

~: Extension of the base of a Cumulonimbus cloud, in the form of funnel, which, circulating fast, goes down to the surface of the Earth, where it produces as strong whirlwind capable of causing great destruction.

~: A violent rotating column of air, extending from the base of a cumulonimbus cloud to the ground, producing damaging winds up to 300 mph.

~- A violently rotating column of air that reaches from the base of a cloud to the ground.
Tropics- The area of the globe from latitudes 23.5 degrees north to 23.5 degrees south.
Tropical Air- Warm, humid air masses that form in tropical regions.

Lines of thunderstorms,
Embedded thunderstorms, and/or
Hail greater than or equal to 3/4" in diameter.

~ - It begins as a funnel cloud with spinning columns of air that drop down from a severe thunderstorm. When they reach the ground they become ~es. ~es are between 300 and 2,000 feet wide and travel at speeds of 20 to 45 miles per hour.

~ - A region of rotation extending from the base of a thunderstorm or other convective cloud to the earth's surface. This is a vortex, or wind velocity field, with a speed of at least 40 MPH at the surface. ~es depend on a parent cloud, such as a thunderstorm, in order to develop.

A ~ Watch is issued by the Storm Prediction Center (SPC) in Norman, Oklahoma. Prior to the issuance of a ~ Watch, SPC will usually contact the affected local National Weather Forecast Office (NWFO) and they will discuss what their current thinking is on the weather situation.

A ~ is a violently rotating column of air in a small range with huge power and extreme damage capability. The diameter of a ~ can range from tens of meters to several hundred meters. In average it is about 250 meters. When seen from afar, it looks like a dark grey funnel or a trunk.

A ~-like rotating column of fire and smoke created by intense heat from a forest fire or volcanic eruption.
Another name for the initial wind surge observed at the surface as the result of downdrafts forming the leading edge or gust front of a thunderstorm.

All ~es, and most other severe local windstorms, are assigned a single number from this scale according to the most intense damage caused by the storm.

Like a ~ Warning, the Severe Thunderstorm Warning is issued by your National Weather Service Forecast Office (NWFO).

Gustfront ~. A small ~, usually weak and short-lived, that occurs along the gust front of a thunderstorm. Often it is visible only as a debris cloud or dust whirl near the ground.

[Slang], a ~ that does not arise from organized storm-scale rotation and therefore is not associated with a wall cloud (visually) or a mesocyclone (on radar).

A ~-like rotating column of fire and smoke created by intense heat from a forest fire or volcanic eruption.

Lines of thunderstorms
Embedded thunderstorms
Large areas of thunderstorms
Large hail
Tropical cyclone
Severe icing
Severe or extreme turbulence
Duststorms and sandstorms lowering visibilities to less that three (3) miles.
Volcanic Ash ...

Weather Forecast Office(Abbrev. WFO) - this type of National Weather Service office is responsible for issuing advisories, warnings, statements, and short term forecasts for its county warning areaWeatherfaxSee RADIOFACSIMILEWedge ~Slang for a large ~ with a condensation ...

Fujita ~ scale Based upon damage patterns, classifies twisters into six categories of wind speed (F0 thru F5), ranging from 40 to 318 mph estimated wind speed, plus a hypothetical F6 with winds from 318 mph to Mach 1. Developed in 1971 by T. Theodore Fujita of the University of Chicago.

Cold-air-funnelA funnel cloud or (rarely) a small, relatively weak ~ that can develop from a small shower or thunderstorm when the air aloft is unusually cold (hence the name). They are much less violent than other types of ~es.

When observed from a distance, they are sometimes mistaken for ~es. SEA BREEZE A diurnal coastal breeze that blows onshore, from the sea to the land. It is caused by the temperature difference when the surface of the land is warmer than the adjacent body of water.

Note particularly the development of the cloud/s giving rise to the thunderstorm/~/waterspout/etc. What we are looking for is the rapidity of build of the cloud; its vertical extent in a noted time. Is it building directly upwards, or sheared to one side?

These may produce some heavy rain, hail, or even a weak ~, but they are usually short-lived (30 minutes or less). The second type is known as a multicell cluster composed of a group of convective clouds that move together as a single unit.

Wedge (or Wedge ~)
[Slang], a large ~ with a condensation funnel that is at least as wide (horizontally) at the ground as it is tall (vertically) from the ground to cloud base. The term "wedge" often is used somewhat loosely to describe any large ~.

Cyclone - In general use the term cyclone is applied to any storm, especially violent, small scale circulations such as ~s, waterspouts, and dust devils.

Enhanced wording - An option used by in some ~ and severe thunderstorm watches when the potential for strong to violent ~es, or unusually widespread damaging straight-line winds, is considered high.

Listed weather types include ~, waterspout, funnel cloud, thunderstorm and severe storm, liquid precipitation (drizzle, rain, rain showers), freezing precipitation (freezing drizzle, freezing rain), and frozen precipitation (snow, snow pellets, snow grains, hail, ice pellets, ice crystals).

Severe Thunderstorm-Any one of the three conditions must be met. 1) ~es 2) Hailstones larger than 3/4" 3) Wind gusts greater than 58 miles per hours.

Doppler radar: weather radar system that employs the apparent shift in frequency of radio waves to perceive air motion and consequently predict ~es and precipitation sooner than previous radars, as well as measure the speed and direction of rain and ice.
(return to top)E ...

counterclockwise (in the Northern Hemisphere) as would be seen from above. Nearly all mesocyclones and strong or violent ~es exhibit cyclonic rotation, but some smaller vortices such as gustnadoes occasionally rotate anticyclonically (clockwise). Compare with anticyclonic rotation.

Suction vortices Small, rapidly rotating whirls perhaps 10 meters in diameter that are found within large ~es.
Sulfur dioxide (SO2) A colorless gas that forms primarily in the burning of sulfur-containing fossil fuels.

Mesocyclone - A storm-scale region of rotation, typically around 2-6 miles in diameter. The circulation of a mesocyclone covers an area much larger than the ~ that may develop within it.

Post-storm Report: A report issued by a local National Weather Service office summarizing the impact of a tropical cyclone on its forecast area. These reports include information on observed winds, pressures, storm surges, rainfall, ~es, damage and casualties.

A small whirling storm over water which can either be spawned from the base of a thunderstorm, or formed in a cold outbreak of Arctic air. They are similar, but generally no as severe as ~es.
Wave Direction ...

Cyclone A severe tropical storm (i.e., winds >64 knots) in the Indian Ocean and Bay of Bengal. See also Hurricane and Typhoon. The term is also applied to closed circulations in the mid latitudes and also popularly to small scale circulations such as ~es.

as commonly used in weather observing practice, an observable occurrence of particular physical significance within the atmosphere; from the viewpoint of weather observations, the atmospheric phenomena include all hydrometeors (precipitation types and fogs), blowing snow, thunderstorms, ~es, ...

There is also a special type of Precipitation mode sometimes called "Severe Weather" mode. This mode operates like normal precip mode, but utilizes VCP11 and produces an image about every 5 minutes. This mode is only used for research or for extreme weather events like hurricanes or ~es.

See also: See also: What is the meaning of Storm, Weather, Thunder, Thunderstorm, Cloud?

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