Meteorology. Team of 2 One calculator – non-programmable One sheet of paper with notes front and back May be computer generated 50 minutes of competition Audubon Weather Guide (meteorology) Bio/Earth CD. WWW.wikispaces.com ScienceFrizzle. Competition. Tests –from previous years
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Meteorology • Team of 2 • One calculator – non-programmable • One sheet of paper with notes front and back • May be computer generated 50 minutes of competition Audubon Weather Guide (meteorology) Bio/Earth CD
WWW.wikispaces.com • ScienceFrizzle
Competition • Tests –from previous years • Available on SO site • See rules for event
Research has revealed that tornadoes usually form under certain types of atmospheric conditions. Those conditions can be predicted, but not perfectly. When forecasters see those conditions, they can predict that tornadoes are likely to occur. However, it is not yet possible to predict in advance exactly when and where they will develop, how strong they will be, or precisely what path they will follow.
The damage from tornadoes comes from the strong winds they contain. It is generally believed that tornadicwindspeeds can be as high as 300 mph in the most violent tornadoes. Windspeeds that high can cause automobiles to become airborne, rip ordinary homes to shreds, and turn broken glass and other debris into lethal missiles. The biggest threat to living creatures (including humans) from tornadoes is from flying debris and from being tossed about in the wind. • Tornadoes are classified according to the damage they cause. Through observational studies, T. Theodore Fujita created the following scale in the late 1960's to classify tornadoes. The scale correlates wind speeds with damage: F-0 is the weakest and F-5 the strongest.
Tornado Basics • What is a tornado? • A tornado is a narrow, violently rotating column of air that extends from the base of a thunderstorm to the ground. Because wind is invisible, you can't always see a tornado. A visible sign of the tornado, a condensation funnel made up of water droplets, sometimes forms and may or may not touch the ground during the tornado lifecycle. Dust and debris in the rotating column also make a tornado visible and confirm its presence. • What is known? • Tornadoes are the most violent of all atmospheric storms. • There are two types of tornadoes: those that come from a supercell thunderstorm, and those that do not. • Tornadoes that form from a supercell thunderstorm are the most common, and often the most dangerous. A supercell is a long-lived (greater than 1 hour) and highly organized storm feeding off an updraft (a rising current of air) that is tilted and rotating. This rotating updraft - as large as 10 miles in diameter and up to 50,000 feet tall - can be present as much as 20 to 60 minutes before a tornado forms. Scientists call this rotation a mesocyclone when it is detected by Doppler radar. The tornado is a very small extension of this larger rotation. Most large and violent tornadoes come from supercells.
CONDENSATION FUNNEL - A funnel-shaped cloud associated with rotation and consisting of condensed water droplets (as opposed to smoke, dust, debris, etc.) • SUPERCELL - A thunderstorm with a persistent rotating updraft. Supercells are rare, but are responsible for a remarkably high percentage of severe weather events - especially tornadoes , extremely large hail and damaging straight-line winds. They frequently travel to the right of the main environmental winds (i.e., they are right movers). Radar characteristics often (but not always) include a hook or pendant, bounded weak echo region (BWER), V-notch, mesocyclone, and sometimes a TVS. Visual characteristics often include a rain-free base (with or without a wall cloud), tail cloud, flanking line, overshooting top, and back-sheared anvil, all of which normally are observed in or near the right rear or southwest part of the storm. Storms exhibiting these characteristics often are called classic supercells; however HP storms and LP storms also are supercell varieties.
UPDRAFT - A small-scale current of rising air. If the air is sufficiently moist, then the moisture condenses to become a cumulus cloud or an individual tower of a towering cumulus or Cb. • MESOCYCLONE - A storm-scale region of rotation, typically around 2-6 miles in diameter and often found in the right rear flank of a supercell (or often on the eastern, or front, flank of an HP storm). The circulation of a mesocyclone covers an area much larger than the tornado that may develop within it.
Non-supercell tornadoes are circulations that form without a rotating updraft. One non-supercell tornado is the gustnado, a whirl of dust or debris at or near the ground with no condensation funnel, which forms along the gust front of a storm. Another non-supercell tornado is a landspout. A landspout is a tornado with a narrow, rope-like condensation funnel that forms when the thunderstorm cloud is still growing and there is no rotating updraft - the spinning motion originates near the ground. Waterspouts are similar to landspouts, except they occur over water. Damage from these types of tornadoes tends to be F2 or less.
GUSTNADO - [Slang], gust front tornado. A small tornado, 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. Gustnadoes are not associated with storm-scale rotation (i.e. mesocyclones ); they are more likely to be associated visually with a shelf cloud than with a wall cloud. • LANDSPOUT - [Slang], a tornado that does not arise from organized storm-scale rotation and therefore is not associated with a wall cloud (visually) or a mesocyclone (on radar). Landspouts typically are observed beneath Cbs or towering cumulus clouds (often as no more than a dust whirl), and essentially are the land-based equivalents of waterspouts.
How do tornadoes form? • Scientists have learned a lot about tornadogenesis from theoretical studies, field projects and physical models – but tornadogenesis – the way tornadoes form – has vexed researchers for decades. • SUPERCELL TORNADOGENESIS A rotating updraft is a key to the development of a supercell, and eventually a tornado. There are many ideas about how this rotation begins. One way a column of air can begin to rotate is from wind shear – when winds at two different levels above the ground blow at different speeds or in different directions. • An example of wind shear that can eventually create a tornado is when winds at ground level, often slowed down by friction with the earth's surface, come from the southwest at 5 mph. But higher up, at 5000 feet above the same location, the winds are blowing from the southeast at 25 mph! An invisible "tube" of air begins to rotate horizontally. Rising air within the thunderstorm tilts the rotating air from horizontal to vertical – now the area of rotation extends through much of the storm. • Once the updraft is rotating and being fed by warm, moist air flowing in at ground level, a tornado can form. There are many ideas about this too.
SHEAR - Variation in wind speed (speed shear) and/or direction (directional shear) over a short distance. Shear usually refers to vertical wind shear, i.e., the change in wind with height, but the term also is used in Doppler radar to describe changes in radial velocity over short horizontal distances.
More Ideas About SupercellTornadogenesis • Scientists are actively trying to prove or disprove a number of tornadogenesis hypotheses. It is complicated science that draws on information from observations, theory, and mathematical and physical models. These are some basic ideas (basic to a scientist, that is) about the processes that might cause tornadoes to form from supercells: • Dynamic Pipe Effect Development of a tornado begins when horizontal winds coming together from different directions are strong 3-4km above the ground and weak or absent near the ground. The result is that rotation first increases aloft. The young tornado will build downward by something called the dynamic pipe effect (DPE): air can not enter through the sides of this belt of rotating air, but can pass through its ends like a pipe. The partial vacuum created within the pipe draws weakly rotating air up into the pipe's lower end. This causes the air to spin faster and eventually become part of the pipe. New sections on the rotating pipe form at lower and lower altitudes through this same process until the pipe (tornado) is in contact with the ground. • Another type of tornado development occurs when converging horizontal winds have the same windspeed through all levels in the thunderstorm. Rotation increases all at once and spans several kilometers along the vertical pipe. The tornado, in this case, forms nearly independent from how high it is above the ground, and develops very rapidly from the ground, up. • Rear Flank Downdraft (RFD) The Rear Flank Downdraft (RFD) may play a role in tornadogenesis. The RFD is a region of dry air pushed towards the ground by the thunderstorm on the backside of, and wrapping around a rotating updraft, and eventually the tornado. It is often visible as a clear slot wrapping around a wall cloud (a persistent lowering from a rain-free base of the main thunderstorm). On radar, the presence of a hook or a small feature hanging from the thunderstorm may indicate the presence of an RFD. Scientists think the RFD may play a significant role in determining the development of a tornado, how long it lasts, and how intense it is. Some scientists think that the RFD, by wrapping around the low-level rotating updraft, forces the rotation to concentrate and lower to the ground.
We still have many questions. Scientists know from field studies that perhaps as few as 20 percent of all supercell thunderstorms actually produce tornadoes. Why does one supercell thunderstorm produce a tornado and another nearby storm does not? What are some of the causes of winds moving at different speeds or directions that create the rotation? What are other circulation sources for tornadoes? What is the role of downdrafts (a sinking current of air) and the distribution of temperature and moisture (both horizontally and vertically) in tornadogenesis? Scientists hope to learn more about the processes that create wind shear and rotation, tilt it vertically, and concentrate the rotation into a tornado when they participate in a large field experiment in 2007. • And, since not all tornadoes come from supercells, what about tornadogenesis in non-supercell thunderstorms? • NON-SUPERCELL TORNADOGENESIS A non-supercell tornado does not form from organized storm-scale rotation. These tornadoes form from a vertically spinning parcel of air already occurring near the ground, about 1-10 km in diameter, that is caused by wind shear from a warm, cold, or sea breeze front, or a dryline. When an updraft moves over the spinning, and stretches it, a tornado can form. Eastern Colorado experiences non-supercell tornadoes when cool air rushes down off the Rocky Mountains and collides with the hot dry air of the plains. Since these types of tornadoes happen mostly over scarcely populated land, scientists are not sure how strong they are, but they tend to be small. Waterspouts and gustnadoes are formed in this way too.
DOWNDRAFT - A small-scale column of air that rapidly sinks toward the ground, usually accompanied by precipitation as in a shower or thunderstorm. A downburst is the result of a strong downdraft. • DRY LINE - A boundary separating moist and dry air masses, and an important factor in severe weather frequency in the Great Plains. It typically lies north-south across the central and southern high Plains states during the spring and early summer, where it separates moist air from the Gulf of Mexico (to the east) and dry desert air from the southwestern states (to the west). The dry line typically advances eastward during the afternoon and retreats westward at night. However, a strong storm system can sweep the dry line eastward into the Mississippi Valley, or even further east, regardless of the time of day. A typical dry line passage results in a sharp drop in humidity (hence the name), clearing skies, and a wind shift from south or southeasterly to west or southwesterly. (Blowing dust and rising temperatures also may follow, especially if the dry line passes during the daytime. These changes occur in reverse order when the dry line retreats westward. Severe and sometimes tornadic thunderstorms often develop along a dry line or in the moist air just to the east of it, especially when it begins moving eastward.
Tornado Climatology • Where and when do tornadoes occur? • Tornadoes occur in many parts of the world, including Australia, Europe, Africa, Asia, and South America. Even New Zealand reports about 20 tornadoes each year. • Two of the highest concentrations of tornadoes outside the U.S. are Argentina and Bangladesh. Both have similar topography with mountains helping catch low-level moisture from over Brazil (Argentina) or from the Indian Ocean (Bangladesh). • About 1,000 tornadoes hit the U.S. yearly. Since official tornado records only date back to 1950, we do not know the actual average number of tornadoes that occur each year. Plus, tornado spotting and reporting methods have changed a lot over the last several decades.
A recent NSSL study, using data from 1921 to 1995, estimated the daily climatological probability of an F2 or greater tornado occurring near any location in the U.S. For this work developing highly accurate and accessible estimates of the long-term threat from thunderstorms, winds, and large hail as well as tornadoes, an NSSL scientist was awarded a Department of Commerce Silver Medal. Probability of Any Tornado:The map shows the average number of days per year any tornado, no matter how strong or weak, might occur within 25 miles of a point. The highest numbers indicate where at least one tornado might occur somewhere within 25 miles as often as on 1.5 days per year.
Significant Tornado (F2 or greater):Now we're looking at days per century. In other words, central Oklahomans can expect an F2 or greater tornado within 25 miles about every 3 years.
Violent Tornado (F4 or greater):Now the scale is days per millennium, meaning that southcentral Oklahoma may have a violent tornado within 25 miles about once every 20 years.
Annual Cycle:Residents of Norman, OK experience a distinct tornado season, beginning late February and peaking late May. Even though we are in the heart of tornado alley and can expect one- to one-and one-half tornado days per year, our chances on any particular day peak at only about two percent.
Tornado season usually refers to the time of year where the U.S. sees the most tornadoes. The peak “tornado season” for the southern plains -- often referred to as Tornado Alley -- is during May into early June. On the Gulf coast, it is earlier during the spring. In the northern plains and upper Midwest, tornado season is in June or July. But, remember, tornadoes can happen at any time of year. Tornadoes can also happen at any time of day, but most tornadoes occur between 4-9 p.m.
Tornado Alley is a nickname for an area that consistently experiences a high frequency of tornadoes each year. The area that has the most strong and violent tornadoes includes eastern SD, NE, KS, OK. Northern TX, and eastern Colorado. The relatively flat land in the Great Plains allows cold dry polar air from Canada to meet warm moist tropical air from the Gulf of Mexico. A large number of tornadoes form when these two air masses meet, along a phenomenon known as a "dryline." • The dryline is a boundary separating hot, dry air to the west from warm, moist air to the east. You can see it on a weather map by looking for sharp changes in dew point temperatures. Between adjacent weather stations the differences in dew point can vary by as much as 40 degrees or more. The dryline is usually found along the western high plains. Air moving down the eastern slopes of the Rockies warms and dries as it sinks onto the plains, creating a hot, dry, cloud-free zone. During the day, it moves eastward mixing up the warm moist air ahead of it. If there is enough moisture and instability in the warm air, severe storms can form - because the dryline is the "push" the air needs to start moving up! During the evening, the dryline "retreats" and drifts back to the west. The next day the cycle can start all over again, until a larger weather system pushes through and washes it away.
Tornadoes kill an average of 60 people per year, mostly from flying or falling debris. • The Tri-State Tornado of March 18, 1925 was the deadliest tornado in history, killing 695 people. It is also the longest tornado track ever known - 219 miles - across parts of Missouri, Illinois and Indiana. • Codell, KS was struck by a tornado on May 20 three years in a row: 1916, 1917, and 1918. • Understanding the threat posed by tornadoes in the United States - particularly the threat of strong and violent tornadoes - is valuable knowledge to everyone, but especially to weather forecasters and emergency management people. Knowledge about long-term patterns helps us be better prepared for natural disasters and could also help scientists detect shifting patterns in severe weather events caused by climate change.
Floods • Flood Basics • What is flooding? • Flooding is an overflowing of water onto land that is normally dry. It can happen during heavy rains, when ocean waves come onshore, when snow melts too fast, or when dams or levees break. Flooding may happen with only a few inches of water, or it may cover a house to the rooftop. The most dangerous flood event, the flash flood, happens quickly with little or no warning; other flooding events occur over a long period and may last days, weeks, or longer. • What is a river flood? • A river flood occurs when water levels rise in a river due to excessive rain from tropical systems making landfall, persistent thunderstorms over the same area for extended periods of time, combined rainfall and snowmelt, or an ice jam.
What is coastal flooding? • Coastal flooding occurs when a hurricane, tropical storm, or tropical depression produces a deadly storm surge that overwhelms coastal areas as it makes landfall. Storm surge is water pushed on shore by the force of the winds swirling around the storm. This advancing surge combines with the normal tides to create the hurricane storm tide, which can increase the average water level 15 feet or more. The greatest natural disaster in the United States, in terms of loss of life, was caused by a storm surge and associated coastal flooding from the great Galveston, Texas, hurricane of 1900. At least 8,000 people lost their lives. • What is inland flooding? • When tropical cyclones move inland, they are typically accompanied by torrential rain. If the decaying storm moves slowly over land, it can produce rainfall amounts of 20 to 40 inches over several days. Widespread flash flooding and river flooding can result. • What is a flash flood? • A flash flood is a rapid rise of water along a stream or low-lying urban area. Flash flooding occurs within six hours of a significant rain event and is usually caused by intense storms that produce heavy rainfall in a short amount of time. Excessive rainfall that causes rivers and streams to swell rapidly and overflow their banks is frequently associated with hurricanes and tropical storms, large clusters of thunderstorms, supercells, or squall lines. Other types of flash floods can occur from dam or levee failures, or a sudden release of water held by an ice jam. Heavy rainfall in the mountains can cause downstream canyon flooding. • Why is a flash flood so dangerous? • Flash floods can occur with little or no warning. Flash flood damage and most fatalities tend to occur in areas immediately adjacent to a stream or arroyo. Flash floods are very strong -- they can roll boulders, tear out trees, destroy buildings and bridges, and scour out new channels. Rapidly rising water can reach heights of 30 feet or more. Flash flood-producing rains falling on steep terrain can weaken soil and trigger catastrophic mud slides that damage homes, roads, and property.
What areas are at risk from flash floods? • Densely populated areas are at a high risk for flash floods. The construction of buildings, highways, driveways, and parking lots increases runoff by reducing the amount of rain absorbed by the ground. This runoff increases the flash flood potential. • Sometimes, streams through cities and towns are routed underground into storm drains. During heavy rain, the storm drains can become overwhelmed and flood roads and buildings. Low spots, such as underpasses, underground parking garages, and basements can become death traps. • Areas near rivers are at risk from flash floods. Embankments, known as levees, are often built along rivers and are used to prevent high water from flooding bordering land. In 1993, many levees failed along the Mississippi River, resulting in devastating flash floods. The city of New Orleans experienced massive devastating flooding days after Hurricane Katrina came onshore in 2005 due to the failure of levees designed to protect the city.
Hail • Hail Basics • What is hail? • Hail is a form of precipitation that occurs when updrafts in thunderstorms carry raindrops upward into extremely cold areas of the atmosphere where they freeze into ice. • How does hail form? • There are two ideas about hail formation. In the past, the prevailing thought was that hailstones grow by colliding with supercooled water drops. Supercooled water will freeze on contact with ice crystals, frozen rain drops, dust or some other nuclei. Thunderstorms that have a strong updraft keep lifting the hailstones up to the top of the cloud where they encounter more supercooled water and continue to grow. The hail falls when the thunderstorm's updraft can no longer support the weight of the ice or the updraft weakens. The stronger the updraft the larger the hailstone can grow.
SUPERCOOLED WATER - Liquid water that is below 0°C, or water that stays in liquid form if undisturbed even though it has been cooled to a temperature below its normal freezing point. The smaller and purer the water droplets, the more likely they can become supercooled.
Recent studies suggest that supercooled water may accumulate on frozen particles near the back-side of the storm as they are pushed forward across and above the updraft by the prevailing winds near the top of the storm. Eventually, the hailstones encounter downdraft air and fall to the ground. • Hailstones grow two ways: by wet growth or dry growth processes. In wet growth, a tiny piece of ice is in an area where the air temperature is below freezing, but not super cold. When the tiny piece of ice collides with a supercooled drop, the water does not freeze on the ice immediately. Instead, liquid water spreads across tumbling hailstones and slowly freezes. Since the process is slow, air bubbles can escape resulting in a layer of clear ice. • Dry growth hailstones grow when the air temperature is well below freezing and the water droplet freezes immediately as it collides with the ice particle. The air bubbles are "frozen" in place, leaving cloudy ice. • Hailstones can have layers like an onion if they travel up and down in an updraft, or they can have few or no layers if they are "balanced" in an updraft. One can tell how many times a hailstone traveled to the top of the storm by counting the layers. Hailstones can begin to melt and then re-freeze together - forming large and very irregularly shaped hail.