Meteorology

1. Meteorology (4) Severe Storms: Thunderstorms, Tornadoes and Hurricanes

3. Thunderstorms • A thunderstorm affects a relatively small area when compared to a hurricane or a winter storm. The typical thunderstorm is 15 miles in diameter and lasts an average of 30 minutes. (from nws.noaa.gov) • Despite their small size, ALL thunderstorms are dangerous! Of the estimated 100,000 thunderstorms that occur each year in the United States, about 10 percent are classified as severe.(from nws.noaa.gov) • T-storms generate lightning and thunder

4. What Are Thunderstorms? What Causes Them? • Every Thunderstorm Needs: • ■Moisture—to form clouds and rain • ■Unstable air—warm air that can rise rapidly • ■Lift—caused by cold or warm fronts, sea breezes, mountains, or the sun’s heat • T-storms form when warm, humid air rises in an unstable environment

5. 3 Stages of a Thunderstorm Red arrows = rising warm air; Blue arrows = sinking cold air Updrafts of warm air cause the cloud to grow upward Heavy precipitation falls The storm cools and dies down #3 = C #4 = A #5 = B

7. Tornadoes • These violently rotatingcolumns of air (vortexes) usually only last a few minutes, but they can be catastrophic events; lasting for more than an hour and traveling dozens of miles. Most of the world’s tornadoes occur in the United States and usually these natural hazards occur between April and June(spring).

8. Tornado Formation • Exactly how and why tornadoes form is not completely understood. What is known is that most result from supercell thunderstorms. These severe thunderstorms have persistent updrafts that can reach speeds of 100 mph. Within the storm, a strong vertical wind shear causes a horizontally rotating cylinder of air (Figure a). The updraft lifts the rotating cylinder within the supercell (Figure b). **The rotating cylinder of air narrows, becoming stretched, and spins faster and faster forming a tornado (Figure c). The rotation within the thunderstorm gives the supercell its classic "hook" appearance which can be seen on radar.

9. Tornado Formation

10. Tornado Alley

11. Fujita Scale

12. Watches and Warnings • A watch is issued when there is a possibility of a tornado • A warning is issued when a tornado has actually been seen/has been sighted somewhere nearby • Animations of tornadoes

14. Hurricanes • A hurricane is a tropical cyclone (counterclockwise movement of air) characterized by sustained winds of 120 kilometers per hour (75 miles per hour) or greater. • Hurricanes are the most powerful storms on Earth: think about their size, wind intensity, amount of rainfall and storm surge. • As more and more people live and work in coastal areas, the threat of damage and personal injuries keeps growing. • Hurricanes usually develop in late summer because they are fueled by heat and moisture from warm water. When a hurricane’s eye lands, a dome of water about 65 to 80 km wide called a storm surge sweeps across the coast. • A hurricane may weaken when it moves over cool ocean water, and when it moves over land.

17. Stages of Development • "Tropical cyclone" is a generic term for any organized low pressure system that develops over tropical and sometimes subtropical waters. Tropical depressions, tropical storms, and hurricanes are examples of tropical cyclones. On average, it takes about five days for a tropical cyclone to reach its maximum potential intensity. The following terms are stages of tropical cyclones in order of development. • Tropical wave -- A low pressure trough of persisting winds that blow from east to west. • 1)Tropical disturbance-- An organized area of thunderstorms generally 100-300 miles in diameter. Typically, a tropical disturbance maintains its identity for at least 24 hours and is accompanied by heavy rains and gusty winds. • 2)Tropical depression-- An organized area of tropical low pressure in which sustained winds are 38 miles per hour or less. • 3)Tropical storm-- A tropical cyclone with maximum sustained wind speeds of 39-73 miles per hour and accompanied by thunderstorms. • 4)Hurricane-- A tropical cyclone with maximum sustained winds of at least 74 miles per hour and accompanied by thunderstorms. In the Northern Hemisphere, hurricane winds circulate in a clockwise rotation. • information taken from weather.com

18. Saffir-Simpson Scale Wind Speed Animation Storm Surge Animation

19. Severe Storms