Storms • A storm is a violent disturbance in the atmosphere • 4 major types of storms: – Thunderstorms – Tornadoes – Hurricanes – Winter Storms • A meteorologist is a scientist who studies weather and tries to predict it
Thunderstorms How Thunderstorms Form • For a thunderstorm to form, three conditions must exist. 1. There must be an abundant source of moisture in the lower levels of the atmosphere. 2. Some mechanism must lift the air so that the moisture can condense and release latent heat. 3. The portion of the atmosphere through which the cloud grows must be unstable.
Thunderstorms happen when a cold front meets a warm front, and a cumulonimbus cloud forms The air near the Earth’s surface must be warm and moist The atmosphere must be unstable
Thunderstorms • Warm, humid air rises rapidly and the air cools, forming dense thunderhead clouds • Heavy rain falls, sometimes along with hail • Within the thunderhead cloud there are strong updrafts and downdrafts
Thunderstorms • Lightning heats the air to 30, 000 o. C • Thunder is the sound of the rapidly heated air expanding suddenly and explosively • Light travels faster than sound so you see lightning before you hear thunder
Lightning can be over 50, 000 degrees F Record for being hit by lightning— 7 times!
Lightning • Lightning is a sudden spark, or electrical discharge • Positive and negative charges jump between parts of a cloud, or between nearby clouds, or between a cloud and the ground
Lightning Strikes in the U. S. • This map shows how often lightning strikes different parts of the lower 48 states. Central Florida has the most intense concentration of cloud-to-ground lightning because it has a lot of warm, humid air. The Pacific Northwest has almost no lightning.
Calculating Lightning Distances • Watch the sky for a flash of lightning. • Count the number of seconds until you hear thunder. • Divide the number of seconds by 5 to calculate the distance the storm is away from your location in miles (or divide by 3 for kilometers). • Ex: If you counted 18 seconds from when you saw the lightning, the strike was 3. 6 miles (6 kilometers) from your location. Divide Number of Seconds by 3 for Distance in Km or 5 for Distance in Miles.
�Hail is only produced by cumulonimbus clouds Hail ◦ Water in the cloud freezes onto dust or dirt ◦ The ice ball falls in the cloud, gets blown back up, and gathers more ice �Ice forms in layers in hail, like an onion ◦ Eventually, the hail gets too heavy to get blown around anymore, and falls to Earth ◦ Hail can be over 6 inches around and weigh more than a pound!
Safety Lightning kills more people than tornadoes or hurricanes Stay away from metal objects and tall structures If you are outside, get down flat on the ground, and don’t touch other people • Lightning can jump from one person to another
Tornadoes • Violent low pressure windstorms that take the form of a vortex. • Vortex- spinning/rotating, often turbulent, column of air • The vortex extends downward from a cumulonimbus cloud – produce rain and hail • Move counterclockwise
Tornado Formation • Warm, moist air flows in at the bottom of a cumulonimbus cloud and moves upward • A low pressure area forms inside the cloud • Warm air rotates as it meets winds blowing in different directions at different altitudes
How a tornado occurs: Tornado formation: • Wind starts traveling in 2 different directions • This causes a layer of air in the middle to rotate like a toilet paper roll
How a tornado occurs: • Finally, when the funnel cloud reaches the ground, it’s called a tornado
Where they happen Most of the world’s tornadoes (75%) occur in the US – Tornado Alley—The part of the Plain States in the US where tornadoes are most frequent
• Tornado Alley is an area of the United States that has a high frequency of tornadoes because cold, dry air moves south from Canada to meet warm, humid air from the Gulf of Mexico • 5 states that cross Tornado Alley are: – – – Texas Oklahoma Kansas Nebraska Iowa
Wind Speeds Winds can be over 300 mph in a tornado In most cases, they’re usually less than 130 mph
Tornado Scale Tornadoes are ranked from F 0 (weak) to F 5 (very, very strong)
Tornadoes in North Carolina Average per year: 16 Average per 10, 000 sq. miles: 3. 26 Most in One Year: 66 in 1998 Average Tornado Deaths per year: 2 Average Tornado Injuries per year: 39 Deadliest Tornado: February 19, 1884, a tornado in Anson and Richmond Counties • killed 23 people. • • •
F 4 tornados in NC from 1950 North Carolina has never had a recorded F 5 tornado • However, we’ve had about 27 F 4 tornadoes since 1950 • The most recent F 4 was in Caldwell County on May 7, 1998
Safety • There may be a tornado when: – Conditions are right for a thunderstorm – The sky may be a greenish color
Safety • Tornado watch: Conditions are right for a tornado, be aware • Tornado warning: A tornado has been spotted, take cover
Safety How to survive a tornado • Get in the lowest room of the house • Stay away from glass windows or sharp objects • Get in a bathtub, and/or under a mattress • If you’re outdoors, get in a ditch – Under a cement overpass will also work if there’s no ditches, but it can be dangerous • The wind acts like a vacuum, and can suck you out
Fire tornadoes • Very rarely, the conditions are right for tornadoes to form during a fire – The air forms a vertical column of air, creating a fire tornado or “fire whirl” – Fire tornadoes can topple trees up to 50 feet tall. These can also start new fires during a forest fire
Definitions • Hurricane: A large, rotating tropical weather system with wind speeds of at least 70 mph – Can be seen from space – Creates the most powerful storms on Earth – They form in the oceans, and gain speed in warm waters • Over land, they lose energy and fall apart
Hurricanes • Whirling tropical cyclones (low pressure system) producing winds of at least 119 km per hour (73 mph) • US – Hurricanes • Pacific – Typhoons • Indian Ocean – Cyclones • Most powerful storm on Earth
Naming • Hurricanes are named alphabetically every year – Alternate between male and female names – Rotate names on a 7 year basis – Names for very destructive hurricanes are retired and never used again • Examples: Hurricanes Andrew, Hugo, Katrina
Hurricanes • Hurricanes last longer than other storms, usually a week or more • After a hurricane passes over land, it no longer has warm, moist air to draw energy from so it loses strength • A storm surge is a “dome” of water that sweeps across the coast where a hurricane lands • For safety during a hurricane, people are told to evacuate • Evacuate means to leave the area immediately
Formation • How hurricanes form: – Warm air above the water provides energy and makes clouds – Wind forces the air upwards – Clouds and wind start to swirl around, creating a hurricane
Video Parts of a Hurricane Eye: Center of storm, warmest part, winds cease, rain ceases Eye wall: Strongest winds and rain Spiral Rain Bands: extend out from the eye wall
A Hurricane’s “Death” • As a hurricane makes landfall, the supply of warm, moist air that was fueling it is cut off • As the downdrafts and rain cool the land, the strength of the updraft slows • Without an updraft, the system will dissipate, and eventually die out (just like a thunderstorm) • This may take days and 100’s of miles • Hurricane Ike comes to Michigan in 2008 (my front yard in Commerce Township) >
Something to think about • Because of wind patterns due to the turning of the Earth (the Coriolis Effect), hurricanes spin in opposite directions in the different hemispheres – In the Northern Hemisphere, hurricanes (and tornadoes!) spin counterclockwise – In the Southern Hemisphere, hurricanes spin clockwise
Scale • Ranked from: – Tropical depression – Tropical storm – Category 1 – Category 2 – Category 3 – Category 4 Category 5 Strongest What is Storm Surge Video Weakest
Locations • Hurricane season in the Atlantic Ocean runs from June 1 -November 30 th • In the Atlantic Ocean, they’re called hurricanes • In the Pacific Ocean, they are called typhoons • In the Indian Ocean, they’re called cyclones
Hurricanes in North Carolina • North Carolina has a hurricane make landfall along the coastline about once every four years. – An estimated 17. 5% of all North Atlantic hurricanes have affected our state – The largest hurricane to ever hit was Hurricane Hazel in 1954 • Category 4
Hurricane Katrina • As the storm moved across the Gulf of Mexico, it RAPIDLY developed (from a Category II to a Category V in only 9 hours) • Wind speeds reached 175 mph • A mound of water was pushed toward Louisiana and Mississippi… • even though wind speeds slowed (to a Category III) by the time it made landfall
The Aftermath • The most destructive and costliest natural disaster in the history of the US • More than $81 billion dollars in damage • More than 1800 people died (700 still listed as missing) • More than 90, 000 square miles declared a Federal Disaster Area • More than 3 million people were left without power
Additional Effects • There were unforeseen economic effects – Gas and Oil production shutdowns – Unemployment – Insurance Company Bankruptcies – Relocation/Flight from the region • Environmental Effects – – Oil Spills Erosion Sewage Loss of Marine and Animal life • Looting and Violence
Tropical Storms Hurricane Hazards Hurricane Advisories – The National Hurricane Center, which is responsible for tracking and forecasting the intensity and motion of tropical cyclones in the western hemisphere, issues a hurricane warning at least 24 hours before a hurricane strikes. – The center also issues regular advisories that indicate a storm’s position, strength, and movement.
Tropical Storms Hurricane Hazards Hurricane Advisories
How to stay safe during a hurricane How to stay safe: • Have an emergency plan figured out BEFORE the hurricane strikes • Stay away from low lands that could flood • Always stay indoors during a hurricane, as strong winds may blow things around. • Leave mobile homes and go to a shelter. • Stay away from downed power lines • If you get an order to evacuate, then do so immediately.
Definition • Blizzard: A severe winter storm with low temperatures (under 10 degrees), strong winds (over 55 mph), and heavy blowing snow lasting at least 3 hours – Most winter snow storms are NOT blizzards – Blizzards can occur anywhere there is snow and high winds
How Blizzards Form: • Cold, dry Canadian air moves south and mixes with a warm, moist air mass moving north from the Gulf of Mexico • Blizzards need 3 things to form: • The air needs to be cold at the surface • The atmosphere has to have a lot of moisture • There has to be wind to lift the warm air over the cold air.
Whiteouts • Whiteouts: A condition that may happen during a blizzard where shadows, nearby objects, landmarks, clouds, and even the horizon are not visible. • Land sky seem to blend together. • All you see is white! • All sense of direction, depth perception, and even balance may be lost.
Whiteouts • Whiteouts happen when rays of sunlight are bounced in all directions between bright white clouds • Real whiteouts occur mostly in the Arctic and Antarctic during the spring
Effects of Blizzards • Effects of Blizzards: – It may be difficult to see or breathe during a blizzard. – Traffic accidents – Cities may shut down as snow traps people – Possible death from freezing temperatures • The number one cause of death during a winter storm are heart attacks while shoveling
Famous Blizzards • The Blizzard of 1888 • Happened in 1888 in the Northeastern United States. • Snowdrifts reached heights of 15 to 50 feet high. • People were stuck in their houses for over a week • 400 people were killed, and 200 ships sunk
Famous Blizzards • Schoolhouse Blizzard • Happened in 1888 in the Plain States • The day had been calm and mild, and people left their homes to enjoy the warmth • Children got trapped in schoolhouses, and people got stranded at work • Overall, over 500 people were killed
Famous Blizzards • The Armistice Day Blizzard: • Hit New York and surrounding states in 1940 • Caught many people off guard with rapid and extreme temperature change. • It was 60°F in the morning but snowing heavily by noon • Some of those caught unprepared died by freezing to death in the snow and some while trapped in their cars. • 154 people died
Famous Blizzards • The Storm of the Century • Hit the U. S in 1993 • It dropped snow over 26 states and reached as far north as Canada and as far south as Mexico. • In many southern US states, more snow fell in this storm than ever fell in an entire winter. • At least half of the U. S. population was affected • 270 people died and 48 were reported missing at sea.
Safety • To stay safe during a blizzard: • Fill bathtubs with water in case pipes freeze. • Make sure windows and doors are tightly closed anything movable in the yard is tied down or brought inside. • Bring pets indoors as they may not survive the cold temperatures • Stock up on food, especially food that doesn't need to be prepared with electricity • Have batteries for flashlights and radios. • Unless it is absolutely necessary, stay indoors.
Recurring Weather Floods and Droughts • Floods can occur when weather patterns cause even mild storms to persist over the same area. Droughts are extended periods of well-belownormal rainfall. Droughts are usually the result of shifts in global wind patterns that allow large high-pressure systems to persist for weeks or months over continental areas.
Recurring Weather Floods and Droughts Heat Waves – Heat waves, which are extended periods of abovenormal temperatures, can be formed by the same highpressure systems that cause droughts. – As the air under a large high-pressure system sinks, it warms by compression and causes above-normal temperatures. – The high-pressure system also blocks cooler air masses from moving into the area, so there is little relief from the heat.
Recurring Weather Floods and Droughts Heat Waves – If the air is humid, it slows the rate of evaporation, which diminishes the body’s ability to regulate internal temperature. – Because of the danger, the National Weather Service routinely reports the heat index. – The heat index assesses the effect of the body’s increasing difficulty in regulating its internal temperature as relative humidity rises.
Recurring Weather Floods and Droughts
Recurring Weather Cold Waves • A cold wave is an extended period of belownormal temperatures. Cold waves are brought on by large, high-pressure systems of continental polar or arctic origin. Winter high-pressure systems are much more influenced by the jet stream than are summer systems and therefore rarely linger over one area. Several polar high-pressure systems can follow the same path and subject the same areas to bout after bout of numbing cold.
Recurring Weather Cold Waves • The wind-chill factor is measured by the windchill index, which estimates the heat loss from human skin caused by the combination of cold air and wind.