Tornadoes-Purple



Tornadoes Sarah G. and Madison G.  Purple Class

Introduction ==== Tornadoes are violent wind storms that take the shape /form of a rotating column of air called a vortex (3/4/5). The vortex extends out from a cumulonimbus cloud all the way to the ground (5). On average, tornado wind speeds stay under 100mph, however they can top 250mph in extreme conditions, such as the Super Outbreak of 1974 (1/4). These high wind speeds that tornadoes can produce can cause extreme damage, and the amount of damage a tornado inflicts indicates which category it falls under on the Fujita-Pearson scale (3). Tornadoes are actually transparent, however the debree and dust that gets sucked up into the condensation funnel give them their color, thus making them visible as funnel clouds (1/3). There are two main types of tornadoes, supercell tornadoes and non-supercell tornadoes. A supercell tornado is the most dangerous storm, and forms from cumulonimbus clouds (6). Supercell tornadoes can last a long time, sometimes longer than an hour, and can contain updrafts as large as 10 miles in diameter and sometimes 50,000 feet tall (6). Non-supercell tornadoes consist of gustnados, landspouts and waterspouts (6/7). What separates a gustnado from a supercell tornado is the fact that it is only a vortex of air, and doesn't include a condensation funnel (6). These storms form at the gust front of tornadoes, and are a whirl of dust and debris from the ground (6/7). A landspout tornado is a narrow condensation funnel that does not include an updraft, and forms before the thunderstorm cloud has reached its height (6). Lastly, a waterspout tornado forms in identical ways to landspouts, except they form over water (6). All non-supercell tornadoes tend to be the F2 category or under on the Fujita-Pearson scale (6). Overall, although tornadoes can be the smallest form of severe weather, their high wind speeds can at times cause the most damage.====

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Dangers Because Tornadoes are such a severe weather condition, they have the ability to inflict much harm on people and property. The high wind speeds of tornadoes are what can cause much damage to occur, and Tornadoes are categorized on the Fujita-Pearson scale, which categorizes them based upon the damage they create (3). The categorizes of the Fujita-Pearson scale range from F0-F5, F0 causing the least destruction, and F5 causing the most (3). F0 category storms are storms where wind speeds stay below 116mph, and they can cause light damage, for example broken tree branches, chimneys, billboard signs, and uprooted thin trees (5). F1 Tornadoes have wind speeds ranging from 116mph-180pmh, and cause moderate damage (5). They can pull off the surfaces of roads, blow mobile homes from their original positions or tip them, and can blow moving cars off roads (5). F2 Tornadoes are more severe, and can cause considerable damage with wind speeds from about 181mph-253pmh (5). F2 Tornadoes can tear roofs off houses, destroy mobile homes, and even snap/uproot large trees (5). More intense still, F3 storms can cause severe damage such as tearing off roofs and walls of well built homes, tipping over trains, uprooting entire forests, and lifting cars off the ground, with their wind speeds of 254mph-332pmh (5). F4 Tornadoes have winds of 333mph-419mph, and the damage such winds can produce is devastating (5). They can destroy entire well made homes, carry away structures with weak foundations, and toss cars through the air (5). Lastly, the most intense tornadoes are categorized as F5 tornadoes, and cause incredible damage because their wind speeds top 419mph (5). For example, such intense winds can lift strong houses off of their foundations and carry them away, cause automobile sized missals to fly through the sky, and can tear bark off of trees (5). Some universal dangers that can accompany any tornado include flash floods, which are the number one weather killer and can kill on average 146 people annually, lightning, which kills 75-100 people every year, damaging straight line winds, and large hailstones that can reach the size of grapefruits and cause damage of up to several million dollars to buildings and crops (2).

[|Click here] for a before and after view of an area hit by a tornado.



Conditions of Formation ==== Tornadoes are a type of severe weather that can occur any time, anywhere as long as the conditions are right (1). Tornadoes are often associated with thunderstorms and hurricanes/tropical storms due to the fact that with these severe weather conditions come the right conditions for the formation of tornadoes (1/5/7). For example, for a thunderstorm to occur the presence of a cumulonimbus could is needed which is also true for the the occurrence of a tornado (5). The updrafts of the thunderstorm create a mesocyclone--a vertical cylinder of rotating air (3). Strong winds high in the atmosphere, due to differences in pressure because wind flows from areas of high to low pressure, cause the winds in the lower atmosphere to roll (5). Then updrafts from the thunderstorm cause the rolls to tilt so they are nearly vertical. When the rotating columns of air become vertical the conditions needed for tornadoes are present, however most mesocyclones do not result in tornadoes (5). ====

==== Tornadoes generally form along cold fronts, because when a cold front moves through an area previously occupied by a warm front, the pressure gradient becomes very high due to the large differences in air temperature so fast wind speeds occur (4). Furthermore, the air becomes very unstable because of the differences in temperature, which is why uplifting occurs therefore causing the formation of mesocyclones (4). Additionally, the colliding fronts can play a part in lifting the air (4). Frontal wedging is when air becomes lifted because two air masses of different densities collide and one is forced over the other. As the air rises, it will cool to its dewpoint and eventually become saturated (4). When air rises, it cools adiabatically, and as it cools its relative humidity goes up because air's capacity lowers as temperature lowers, so the air becomes saturated. This process allows for thunderstorm clouds, cumulonimbus clouds, to form because when air is saturated it condenses on condensation nuclei in the atmosphere such as dust particles, forming clouds (4). Once the air rises, different wind speeds, caused by density differences because wind blows from areas of high pressure to areas of lower pressure, cause fast rotation to occur, which in turn creates the vortex (mesocylone) that tornadoes spawn from (4). There are two different types of tornadoes, supercell tornadoes, which are more common, and non-supercell tornadoes (6). Supercell tornadoes are associated with the updrafts of a thunderstorm that go along with cumulonimbus clouds (6). An updraft occurs when denser air blows over less dense air, because air flows from higher densities to lower densities, and this process sends the less dense air spiraling upwards, causing an updraft. When this happens, a mesocyclone is formed, which tornadoes can then spawn from (6). The tornadoes that form will be small extensions of a larger, rotating mesocyclone, however these supercells cause more damage than any other tornado (6). The collumn of air that forms the vortex of the supercell is created by two different levels of wind above the ground that blow in different directions or at different speeds (6). This column of air creates the rotation that the updraft ultimately pushed vertical to create the mesocyclone (6). Non-supercell tornadoes consist of gustnadoes, landspouts, and waterspouts. When particles of air are already rotating vertically near the ground due to a dry line or warm/cold sea breeze fronts, or because an updraft moves over the vertically spinning parcle of air, it will stretch it out and form a tornado (6). That is the main basis of which all non-supcell tornadoes are formed (6). The peak of "tornado season" (when the most tornadoes form) for Tornado Ally, in the southern plains of the U.S, is May to early June (6). So many tornadoes form here because the cool, polar air from the north collides with the warm, southern air from the Gulf and which creates the spiraling needed for updrafts because of the low pressures created by the warm front being less dense and therefore pushed up over the cold, denser front (6). Most tornadoes happen in the spring because it's a change of season from a cold winter to a warm summer. During this shift, lots of cold and warm air masses meet, forming the perfect conditions to uplift to create mesocyclones, which can then potentially spawn tornadoes. The air rises because the denser, cooler air masses from the north collide with the warmer, less dense, southern air masses, which sends the warmer air upwards. This can then produce thunderstorms, with cumulonimbus clouds, because air will rise, cool, and condense to form clouds, which are the clouds that when mesocyclones form within, tornadoes happen from. ====

[|Click here] to view an interactive diagram of tornado formation.
Historical Examples

====Over the course of history, extreme tornadoes have caught the attention of the media numerous times. For example, on September 19th, 1967, hurricane Beulah sent 115 tornadoes racing towards south-eastern Texas (3). The devistation these tornadoes caused was worsened because of how unexpected they were. The storm unexpectedily changed direction from the north-eastern quadrient, and the tornadoes were sent in a south-easternly direction (3). The storm spanned from September 19th to the 23rd, and held the record for the most number of tornadoes produced from a hurricane, prior to the Super Outbreak of 1974, whose record still stands today (3). The Super Outbreak was a storm in 1974 that spawned 148 Tornadoes and took the record for most tornadoes formed from a single storm from hurricane Beulah (3). 30 of the 148 tornadoes reached F4 and F5 categories according to the Fujita-Pearson Scale (3). As the weather map below shows, the Super Outbreak resulted in such devastation because the conditions of formation were perfect because the cold front with cool, dry air, displaced the warm front containing warm, moist air, so the warmer air was lifted, resulting in extremely low pressures that were eventually able to form tornadoes. Another historical Tornado was the Carolina Outbreak (2). On March 28th, 1984, during the afternoon, 22 tornadoes formed, killing 57 people and injuring 1,248 (2). 37% of the deaths took place in mobile homes, which as stated above can be destroyed if the tornado reaches the F2 category (2/3). The damage of the Carolina Outbreak was immense, and ended up costing almost 200 million dollars to repair everything that was destroyed (2). However, the Pennsylvania-Ohio Outbreak on May 31, 1985 was perhaps even worse (2). Included were 41 tornadoes, 75 deaths, 1,025 injuries and up to 450 million dollars in damage (2). One additional famous tornado that luckily had less death and injury than both the Carolina and Pennsylvania-Ohio Outbreaks, was the Plains Outbreak (2). On April 26th and 27th in 1991, 54 tornadoes spawned and killed 21 people, 15 of whom died in a mobile home or automobile (2). However, even though there were less deaths, there were still 308 injuries, and it took over 277 million dollars to fix the damage (2). That number is less than the Pennsylvania-Ohio Outbreak, yet still 77 million dollars more costly than the Carolina Outbreak.==== media type="youtube" key="yYtMvY-eOGM" height="315" width="560"

Safety

==== Staying safe during a tornado largely depends on where people may be during a tornado. For example, people in a house, apartment building, or mobile home will all react somewhat differently, however all should be listening for warnings on the radio and/or television (2). Additionally, no matter where people are, if they are in an area with a lot of tornadoes they should have a supply of necessities such as food, water, flashlights, batteries, and more (1). Ideally, if someone is at home during a tornado, the person should move to a small room with little to no windows, or to a room designated for keeping safe during a tornado (1/2). If a person lives in an area where tornadoes are common, s/he may want to consider building a designated "tornado safe" room (2). If someone lives in a mobile home and hears warning of an approaching tornado, s/he should evacuate to a pre-determined safe place, within walking distance from his/her house, that s/he will be able to stay until the storm passes (2). Additionally, people in hotels, apartment buildings, or condominiums, should retreat to an interior hallway of a low level floor in their building (2). If a hallway is not an option, people should move to a closet or small, windowless room (1/2). As last resort, getting under heavy furniture that is away from windows will suffice (1/2). When people are outside, without any way to get into a building when a tornado hits, they should lie flat in a low ground area or depression and wait for the storm to blow over (1). In any situation, people are advised to be on the lookout for dark, often greenish skies, walls of clouds, large hail, and loud roars that may remind one of a freight train, to warn them of possible tornadoes (2). Moreover, people should practice drills so that in the event of an emergency, they have a plan and can stay calm because they know what to do, instead of frantically running around at the last minute (2). [|Click here] for instructions on how to conduct tornado drills that can help keep friends and family safe. ====

[|Click here] and drag the scrubber to the last slide, to view more safety tips on surviving tornadoes. By clicking each scenario, different tips on tornado safety in that situation will pop up.

Sources