The Online Tornado FAQ (by Roger Edwards, SPC)Background photo courtesy NSSL. Last modified 1 May 2. This list of Frequently Asked Questions (FAQ) has been compiled from. SPC as well as basic tornado research information. More material will be added. If you find a link not working or an error of any sort, please e- mail the FAQ author. Watch Simple Creature Online (2017).

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Tornado FAQ is not intended to be a comprehensive guide to tornadoes. Instead, it is a quick- reference summary of tornado knowledge.

Recent books from your local library or a major university library. There are many good websites with tornado information, but also, many inaccurate and unreliable ones. As with any other subject, please proceed with great caution online when investigating tornadoes. Some of the trustworthy sites are linked from the answers below. None of the links to outside websites implies any kind of commercial. SPC. The intent here is to direct you to the best tornado info available, regardless of domain.

There is also a partial list of technical scientific references related to tornadoes for. NOTE: All images found in FAQ pages on this site must be public domain and. However, credit should be given to NOAA for use of images, unless labeled otherwise. What is a tornado? Glossary of Meteorology (AMS 2. Literally, in order for a vortex to.

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Weather scientists haven't found it so simple in practice. Doswell). For example, the difference is unclear between an strong mesocyclone (parent thunderstorm circulation) on the ground, and a large, weak tornado. There is also disagreement as to whether separate ground contacts of the same funnel constitute separate tornadoes. Meteorologists also can disagree on precisely defining large, intense, messy multivortex circulations, such as the El Reno tornado of 2. It is well- known that a tornado may not have a visible funnel. Mobile radars also have showed that tornadoes often extend outside an existing, visible funnel.

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At what wind speed of the cloud- to- ground vortex does a tornado begin? How close must two or more different tornadic circulations become to qualify. There are no firm answers. BACK UP TO THE TOP do tornadoes form? The classic answer- -"warm moist Gulf. Watch Sully Online Free HD. Canadian air and dry air from the Rockies"- -is a gross oversimplification.

Most thunderstorms. SPC "High Risk" outlook. The truth is that we don't fully understand. Tornado formation is believed to be dictated mainly by things which happen on the storm scale, in and around the mesocyclone.

Recent theories and results from the VORTEX programs suggest that once a mesocyclone is underway, tornado. Mathematical modeling studies of tornado formation also indicate that it can happen without such temperature patterns; and in fact, very little temperature variation was observed near some of the most destructive tornadoes in history on 3 May 1. The details behind these theories are given in several of the Scientific References. FAQ. BACK UP TO THE TOP do tornadoes come from? Does the region of the US play a role in path direction?

Tornadoes can appear from any direction. Most move from southwest to northeast, or west to east. Some tornadoes have changed direction amid path, or even backtracked. A tornado can double back suddenly, for example, when its bottom is hit by outflow winds from a thunderstorm's core.] Some areas of the US tend to have more paths from a specific direction, such as northwest in Minnesota or southeast in coastal south Texas.

This is because of an increased frequency of certain tornado- producing weather patterns (say, hurricanes in south Texas, or northwest- flow weather systems in the upper Midwest). BACK UP TO THE TOP hail always come before the tornado? Rain? ? Utter silence?

Not necessarily, for any of those. Rain, wind, lightning, and hail characteristics vary from storm to storm, from one hour to the next, and even with the direction the storm is moving with respect to the observer. While large hail can indicate the presence of an unusually dangerous thunderstorm, and can happen before a tornado, don't depend on it. Hail, or any particular pattern of rain, lightning or calmness, is not a reliable predictor of tornado threat. BACK UP TO THE TOP do tornadoes dissipate? The details are still debated by tornado scientists. We do know tornadoes need a source of instability (heat, moisture, etc.) and a larger- scale property of rotation (vorticity) to keep going.

There are a lot of processes around a thunderstorm which can possibly rob the area around a tornado of either instability or vorticity. One is relatively cold - -the flow of wind out of the precipitation area of a shower or thunderstorm. Many tornadoes have been observed to go away soon after being hit by outflow.

For decades, storm observers have documented the death of numerous tornadoes when their parent circulations. BACK UP TO THE TOP. Not in a literal sense, despite what you may have read in many. By definition (above), a tornado must be in. There is disagreement in meteorology over whether or not multiple ground contacts of the same vortex or funnel cloud mean different tornadoes (a strict interpretation).

In either event, stories of skipping tornadoes usually mean. There was continuous contact between vortex and ground in the path, but it was too weak to do damage. Multiple tornadoes happened, but there was no survey done to precisely separate their paths (very common before the 1.

There were multiple tornadoes with only short separation, but the survey erroneously classified them as one tornado. BACK UP TO THE TOP when two tornadoes come together?

That is more unusual than it seems, because most video that seems to show tornadoes merging actually involves either one tornado, or one among multiple subvortices, going behind another. On those very rare occasions when tornadoes do merge, it usually involves a larger and stronger tornado that simply draws in and absorbs the lesser circulation, then keeps on going. On 2. 4 May 2. 01. FAQ witnessed and photographed a merger of a long- lived, violent tornado with a satellite tornado that had grown about as large and strong, based on mobile Doppler- radar data. That rare and maybe unique event is documented in this formal journal paper. BACK UP TO THE TOPHow long does a tornado last? Tornadoes can last from several seconds to more than an hour.

The longest- lived tornado in history is really unknown, because so many of the long- lived tornadoes reported from the early- mid 1. Most tornadoes last less than 1. The average distance tornadoes have traveled (based on path length data since 1.

BACK UP TO THE TOP. To oversimplify this a bit, a tornado (or any other atmospheric vortex) is the most efficient way to move air from one part of the atmosphere to another on its size and time scale. In fluid flow (whether gas or liquid), a vortex often forms when some kind of instability difference exists between one part of the fluid and another, and that difference is strong enough that the fluid needs to move quickly to restore more stable conditions again. This happens on many scales, from huge midlatitude cyclones to hurricanes, supercells, tornadoes and backyard whirlwinds- -even the vortex that forms above a bathtub drain. Most thunderstorms apparently do not need a vortex as intense and efficient at moving air as a tornado, to fulfill their own function of transporting a plume of initially unstable air from the lower atmosphere to higher levels. Why some thunderstorms go far enough to require a tornado's assistance is a matter of great speculation and debate in meteorology.