24 Science: Storms


Students will reflect on the different types of storms and draw picture of each.

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A blizzard is a long-lasting snowstorm with very strong winds and intense snowfall. You need three things to have a blizzard; cold air at the surface, lots of moisture, and lift. Warm air must rise over cold air.

  • A blizzard is a severe snowstorm that usually has very cold temperatures and high winds. These two conditions create blowing snow.
  • When a blizzard occurs it makes driving or walking very dangerous, because the whiteout conditions make it difficult to see.
  • The National Weather Service defines blizzards as large amounts of falling or blowing snow with winds in excess of 35 mph and visibilities of less than ¼ of a mile for a period of more than 3 hours.
  • Blizzards also create a wind chill effect that can be dangerous. The blowing winds and low temperature can cause frostbite and/or hyperthermia.
  • Blizzards that occur on the East Coast of the United States are known as Nor’easters. Because of the Atlantic Ocean, the storm stalls over the coast and can sometimes last for 24 hours dumping huge amounts of snow over the area.
  • If you are located in an area where blizzards occur, you should make sure you have extra food and supplies. You should also have a radio with extra batteries, candles, a cell phone and lots of blankets. You should also plan on staying inside. Many times, children playing right outside of their homes have gotten lost in the blinding snow.


A derecho is a widespread and long-lived windstorm that is associated with a fast-moving band of severe thunderstorms. They can produce significant damage to property and pose a serious threat life, primarily by downburst winds. To be classified as a derecho, the path length of the storm has to be at least 280 miles long. Widths may vary from 50-300 miles. Derechos are usually not associated with a cold front, but a stationary front. They occur mostly in July, but can occur at anytime during the spring and summer.

Derechos form when all the above atmospheric parameters come together to initialize multiple thunderstorm formation. One of the main ingredients is strong, uni-directional winds throughout the lower atmosphere. These strong winds help to develop an intense gust front ahead of the “pool” of rain cooled air . As the pool of rain cooled air continues to expand it allows the gust front to maintain its strength. The cold pool of air then elongates and a rear inflow jet develops. This causes the updraft to tilt toward the rear of the storm, permitting the storm to expand and conserve its strength over a longer distance. As new storm cells continue to form along the leading gust front the process repeats itself, and the entire Mesoscale Convective System (derecho) can track unimpeded for hundreds of miles causing extensive damage.

Typical ideal setup for derecho development. Many of the derechos that eventually affect the East Coast are progressive derechos that ‘ride’ the ridge and are maintained by the Elevated Mixed Layer; the area north of the upper level ridge is therefore often referred to as “the ring of fire”. (Above right) Conceptual depiction of a mature derecho, showing the rain cooled air, gust front, updraft and typical radar reflectivity pattern.


  • A flood is the submerging of normally dry land by an overflow of water.
  • Depending on their type, floods can develop very slowly over time after extensive rains or in just a few minutes, very quickly, without any sign of rain.
  • Floods can be a localised event affecting a small area of land or a very large disaster that can have an impact on entire islands or river basins.
  • There are many types and ways floods can occur, including, due to overflowing rivers, due to extreme coastal events, by natural or artificial ground saturation from excess rainfall, or by catastrophic failure in infrastructure.
  • River flooding is the most common type of flood event. If the flow rate exceeds the capacity of the river channel then flooding of the surrounding area can occur.
  • Flash floods are extreme versions of a river flooding event. They can occur very quickly, often without warning and with little or no excessive rainfall. Flash floods are the result of a river blockage either natural or artificial (such as a landslide,  glacier, or dam) giving way and releasing a massive amount of built up water.
  • Areal or urban flooding occurs when low-lying impenetrable ground becomes saturated as rainfall cannot run off as quickly as the accumulation of water. For example, on natural drought hardened or frozen farmland, or on concrete paving.
  • Coastal and estuary flooding is caused by high sea tidal surges and waves that damage and infiltrate coastal defences. Severe cases can be caused by tsunami, hurricanes or tropical cyclones.
  • With most cities and towns located at the coast or next to rivers, flood events can be major natural disasters, causing loss of life and damage to land and property.
  • Floods can damage bridges, roads and other transport links. Infrastructure such as buildings, cars and houses can be left saturated or completely taken by the waters. While sewage systems and power grids can be destroyed.
  • After floodwaters recede, land can be contaminated with hazardous material, such as building debris, fuel and untreated sewage. Residents are often left without power or clean drinking water which can lead to outbreaks of diseases.
  • Natural flooding of river plains and deltas each year are essential for farming in many areas of the world as the waters bring nutrient rich silt deposits that create very fertile alluvial soils.
  • Today, advanced computer modelling allows authorities to predict where flooding is likely to occur and how severe it will be.


Hail forms in a complex dance between moisture and wind. Deep within cumulonimbus clouds ice crystals form and begin to fall towards the Earth’s surface. As this happens, wind gusts pick up the ice crystals, pushing them back up high into the clouds. As they begin to again fall down, they continue growing in size. Again, a wind gust might catch the growing hail stones, pushing them back up high into the clouds. This process may be repeated several more times until the hail stones become so large that they are too heavy for the wind to carry, causing them to fall towards the Earth.

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Hurricane is a huge storm! It can be up to 600 miles across and have strong winds spiraling inward and upward at speeds of 75 to 200 mph. Each hurricane usually lasts for over a week, moving 10-20 miles per hour over the open ocean. Hurricanes gather heat and energy through contact with warm ocean waters. Evaporation from the seawater increases their power. Hurricanes rotate in a counter-clockwise direction around an “eye” in the Northern Hemisphere and clockwise direction in the Southern Hemisphere. The center of the storm or “eye” is the calmest part. It has only light winds and fair weather. When they come onto land, the heavy rain, strong winds and large waves can damage buildings, trees and cars.

Hurricane Diagram

Hurricanes only form over really warm ocean water of 80°F or warmer. The atmosphere (the air) must cool off very quickly the higher you go. Also, the wind must be blowing in the same direction and at the same speed to force air upward from the ocean surface. Winds flow outward above the storm allowing the air below to rise. Hurricanes typically form between 5 to 15 degrees latitude north and south of the equator. The Coriolis Force is needed to create the spin in the hurricane and it becomes too weak near the equator, so hurricanes can never form there.

Interesting Facts about Hurricanes

  • Hurricanes rotate counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. This is due to the rotation of the Earth called the Coriolis effect.
  • The letters Q, U, X, Y, and Z are not used for the first letter when naming hurricanes.
  • The names are alternated between boy and girl names.
  • Weather forecasters draw a cone showing where they think the hurricane is most likely to travel.
  • You can always find out the latest information on hurricanes at the website of the National Hurricane Center which tracks and forecasts hurricanes.


When water gets colder than 32 degrees Fahrenheit or zero degrees Celsius, it freezes into ice. As the water gets colder, the molecules of water lose their energy and move more slowly – that’s what it means to be colder. When the molecules move more slowly, it is easier for them to hook on to each other by sharing electrons. When enough of the molecules hook on to each other, they form a pattern that looks like a bunch of hexagons, all locked in together, and that is ice. Because the molecules are all locked into place, ice is hard and stiff.

When water freezes into ice, it takes up about 9 per cent more room than it did when it was water. That’s because when the water molecules are locked together, they are farther apart from each other than when they are bouncing around loose as a liquid. It’s as if you were standing in a crowd of people, and then you were standing in a crowd of people all holding hands with their elbows straight and their arms sticking straight out from their bodies. The people would be further apart than before.

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Lightning is a bright flash of electricity produced by a thunderstorm. All thunderstorms produce lightning and are very dangerous. If you hear the sound of thunder, then you are in danger from lightning. Lightning kills and injures more people each year than hurricanes or tornadoes; between 75 to 100 people.

Lightning is an electric current. Within a thundercloud way up in the sky, many small bits of ice (frozen raindrops) bump into each other as they move around in the air. All of those collisions create an electric charge. After a while, the whole cloud fills up with electrical charges. The positive charges or protons form at the top of the cloud and the negative charges or electrons form at the bottom of the cloud. Since opposites attract, that causes a positive charge to build up on the ground beneath the cloud. The grounds electrical charge concentrates around anything that sticks up, such as mountains, people, or single trees. The charge coming up from these points eventually connects with a charge reaching down from the clouds and – zap – lightning strikes!


Thunder is caused by lightning. When a lightning bolt travels from the cloud to the ground it actually opens up a little hole in the air, called a channel. Once then light is gone the air collapses back in and creates a sound wave that we hear as thunder. The reason we see lightning before we hear thunder is because light travels faster than sound!

If you see dark clouds, then lightning could be present, but the best thing you can do is to listen for thunder. If you hear thunder, then you need to go indoors or get in a car. Don’t be outside, where lightning could strike! If your hair stands on end or your skin starts to tingle, lightning maybe about to strike. Get down on your hands and knees and keep your head tucked in. Do not lay flat, because it can give lightning a better chance of strike you.

  • Thunder is the sound caused by lightning.
  • The intense heat from lightning causes the surrounding air to rapidly expand and create a sonic wave that you hear as thunder.
  • The average temperature of lightning is around 20000 °C (36000 °F).
  • The sound of thunder can be anything from a loud crack to a low rumble.
  • Light travels faster than sound so we see lightning before we hear thunder.
  • The closer you are, the shorter the gap between the lightning and thunder.
  • The speed of sound is around 767 miles per hour (1,230 kilometres per hour).
    The speed of light is around 669600000 miles per hour (1080000000 kilometres per hour).
  • Thunder is difficult to hear at distances over 12 miles (20 kilometres).
  • Thousands of years ago philosophers such as Aristotle believed that thunder was caused by the collision of clouds.
  • Astraphobia is the fear of thunder and lightning.


A tornado is a violent rotating column of air extending from a thunderstorm to the ground. The most violent tornadoes are capable of tremendous destruction with wind speeds of up to 300 mph. They can destroy large buildings, uproot trees and hurl vehicles hundreds of yards. They can also drive straw into trees. Damage paths can be in excess of one mile wide to 50 miles long. In an average year, 1000 tornadoes are reported nationwide.

Tornado  Most tornadoes form from thunderstorms. You need warm, moist air from the Gulf of Mexico and cool, dry air from Canada. When these two air masses meet, they create instability in the atmosphere. A change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere. Rising air within the updraft tilts the rotating air from horizontal to vertical. An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.

Tornado FormationTornado FormationTornado Formation

Several conditions are required for the development of tornadoes and the thunderstorm clouds with which most tornadoes are associated. Abundant low level moisture is necessary to contribute to the development of a thunderstorm, and a “trigger” (perhaps a cold front or other low level zone of converging winds) is needed to lift the moist air aloft. Once the air begins to rise and becomes saturated, it will continue rising to great heights to produce a thunderstorm cloud, if the atmosphere is unstable. An unstable atmosphere is one where the temperature decreases rapidly with height. Atmospheric instability can also occur when dry air overlays moist air near the earth’s surface. Finally, tornadoes usually form in areas where winds at all levels of the atmosphere are not only strong, but also turn with height in a clockwise or veering direction.

Tornadoes can appear as a traditional funnel shape, or in a slender rope-like form. Some have a churning, smoky look to them, and other contain “multiple vortices”, which are small, individual tornadoes rotating around a common center. Even others may be nearly invisible, with only swirling dust or debris at ground levels as the only indication of the tornado’s presence.

It is not fully understood about how exactly tornadoes form, grow and die. Tornado researchers are still trying to solve the tornado puzzle, but for every piece that seems to fit they often uncover new pieces that need to be studied.


A tropical storm is a cyclonic storm which originates from the tropics and has sustained winds ranging between 39 and 73 miles/hour (34 to 63 knots; 63 to 117 kilometers per hour).It is characterized by a low-pressure center and by several thunderstorms which create strong winds and heavy rain.

The term tropical cyclone is sometimes used interchangeably with tropical storm due to its cyclone, an area of closed, circular fluid motion rotating in the same direction as the Earth (counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere).However, a tropical cyclone includes a whole class of weather systems, namely tropical depressions, tropical storms, and even hurricanes.

Like a hurricane, a tropical storm is classified by a sustained wind speed. Notably, the wind speed for a tropical storm must range between 39 and 73 mph (63 to 118 km/h). Beyond this point, it is classified as a hurricane. Also, a tropical storm may cause significant damage when it reaches land. Nevertheless, they play a vital role in nature as they distribute heat from lower latitudes near the equator to higher latitudes.

Image result for tropical storm

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