Module #22 - Thunderstorms, Hurricanes and Tornadoes


1. Watch the following video of the Day: National Geographic - Joplin Tornado Outbreak of 2011 (45 min.)

Be sure to make point form notes from these videos in your digital video journal (Communication). Please make sure this document is SHARED with Mr. Durk. 

2. Read the following information below in Part 1: Background and Terminology. Follow all hyper-links to external websites for activities, demonstrations and videos (if applicable). Copy only KEY information (i.e. the highlighted terms) to your digital notebook (in google docs). Complete the online simulation on the formation and destruction that tornadoes cause.

4. Part 2:  Hurricane or Tornado Case Study (20 marks - Communication & Thinking & Inquiry):  Research an famous hurricane or tornado (i.e. is well known or had a major impact on that region) that has occurred in the past ~ 30 years (since 1985). Create a one page "FACT SHEET" (or use picktochart ideally?) or a brief google website (use google sites or equivalent) about this hurricane or tornado. If you are creating a A FACT SHEET or web page it should  include colour images and it should educate people about that specific event. Include information about geographic location, date, exact conditions, damage, deaths / injuries, atmospheric conditions, etc. Include images, graphs and photographs on your fact sheet. Include all of your references at the bottom of your FACT SHEET. If you are curious as to what a FACT SHEET looks like, here are some examples (but not related to hurricanes or tornadoes). Please share your FACT SHEET or web page with Mr. Durk via the UG Cloud. PLEASE fill in this TABLE to claim your Hurricane or Tornado - FIRST COME, FIRST SERVE. 



If you get done early, you can go to the Culminating Project section of the course and start researching what and how you would like to complete the Final Summative Project for the course (15% of your final grade in CGF 3M1). Topic Selection will take place on Tues. June 7th.

DUE DATE:  Submit all components to Mr. Durk via the UG Cloud before next Module (Wednesday June 8th).

NOTE: This is the last module that will be completed as an individual. Next week, we will be having a Climate Change Conference that will count as TWO modules (but will be completed in small groups).

Part 1: Background and Terminology

Please remember to record all definitions and content in your virtual notebook. Definitions can be found by clicking on highlighted words.


Early stages of a thunderstorm developing.Thunderstorms are the most common violent weather event. Heavy rain and violent winds, coupled with lightning and thunder, are enough to frighten anyone and remind us of the awesome power of nature. A thunderstorm is an intense local storm associated with a tall, dense cumulonimbus clouds in which there are very strong updrafts of air. A typical thunderstorm evolves quite fast on hot summer days.

Courtesy of NOAA











Mature stage of a thunderstorm.The sun heats up the ground and the temperature increases and convection currents form as the hot, humid air starts to rise. Slowly, large cumulus clouds begin to form. Air rises in a single convection cell as a series of bubble-like parcels. As these cells of air rise quickly, they cool and produce precipitation.

As the rising air parcels reach six to 12 kilometres in height, the rising rate slows. Strong winds typically present as such high altitudes drag the cloud top downward, giving the thunderstorm cloud its distinctive anvil shape (resembling an old-fashioned blacksmith’s anvil). The resulting cloud is called a cumulonimbus cloud that is tall, dense, and usually has severe thunderstorms associated with it. Eventually, the water is too heavy for the rising air to hold up, and the rain starts to fall. If water droplets have frozen, hail may form. If the updrafts within the cumulonimbus cloud are strong enough, hail may be forced upwards again and again, gaining more water each time, thus becoming large hailstones. The raindrops themselves are often huge because each drop has increased in size as more and more droplets have joined with it. Hail coming from cumulonimbus clouds causes million of dollars of damage each summer as it destroys crops and damages vehicles. Violent winds associated with cumulonimbus clouds can knock out hydro lines, damage buildings and topple trees. Most storm cells die after about 20 minutes, when the precipitation causes more downdraft than updraft, causing the energy to dissipate (disperse).





Cumulative tracks of all cyclones from 1985 to 2005.The most powerful and destructive type of cyclonic storm is the tropical cyclone, which is known as the hurricane in the western hemisphere, the typhoon in the western Pacific, and a cyclone in the Indian Ocean.

These tropical cyclones need very specific conditions to be able to form. This type of storm develops over oceans in 8 ° to 15 ° N and S of the equator. Tropical cyclones are unable to develop any closer to the equator due to the lack of Coriolis Effect which starts the spinning of all cyclonic storms. The Coriolis Effect causes cyclonic storms to turn towards the poles when no other major winds are present. Sea-surface temperatures must be greater than 27 ° C in order to generate enough heat to fuel a hurricane. As the summer sun heats up the Atlantic Ocean, the seawater is so warm that convection currents develop, forming low pressure cells. Winds blow in to replace the unstable air that has risen high up into the atmosphere. As cyclonic storms build in size, their pressure tends to drop, thus drawing in more air to the low pressure centre. If this low pressure intensifies, the storm grows into a tropical depression. The most common time for tropical cyclones to develop into hurricanes is in late summer and early fall, when the sea surface temperatures are the warmest.

Structure of a hurricane.
Hurricane Epsilon
Courtesy of NASA
Hurricane Epsilon

If wind speeds continue to grow a tropical depression becomes classified into a hurricane when wind speeds reach 117 km/h. The eye of the hurricane is the centre of the storm that develops as it matures. Here, air slowly sinks from higher altitudes so there is little wind nor any clouds within the eye. When the eye passes over an area, it is very calm outside and appears that the hurricane may be over. However, this brief period of calm quickly ends as the other side of the eyewall approaches. The eyewall is a band around the eye of greateset wind speed where the clouds reach the highest and precipitation is the heaviest. When hurricanes reach land, the eyewall is where the greatest damage occurs. Bands of showeres and thunderstorms spiral towards the storm centre, drawing in heat and moisture. Tornadoes often form in the rainbands of landfalling hurricanes. Surprisingly, hurricanes do not move quickly over areas and average around 20 km/h in their movement across the ocean or land. Hurricanes are the largest storms on earth, and can be 1000 km in diameter and last up to two weeks!

Hurricanes are the largest storms on earth, can be 1000 kilometres in diameter, and last up to two weeks!

The impact of hurricanes on humans is immense. Flooding kills most of a hurricanes victims, especially close to the coast. Hurricanes cause an increase in sea levels, due to the extremely low pressure and the build up of water from the strong winds. This unusually high water level associated with hurricanes is known as a storm surge. Hurricanes are ranked according to their maximum winds using the Saffir-Simpson Hurricane Scale. A Category 1 storm has the lowest maximum winds (117-153 km/h), while a Category 5 hurricane has the highest (> 249 km/h). The United States National Hurricane Centre classifies hurricanes of Category 3 and above as major hurricanes. he rankings are not absolute in terms of damage and other effects, since it only based on winds speed. Lower category storms can inflict greater damage than higher category storms, depending on factors such as local terrain and total rainfall. For instance, a Category 2 hurricane that strikes a major urban area will likely do more damage than a large

Hurricane Katrina near peak strength on August 28, 2005.

Category 5 hurricane that strikes a mostly rural region. In fact, tropical systems of minimal strength can produce significant damage and human casualties from flooding and landslides, particularly if they are slow moving or very large in size. The National Hurricane Centre in the United States alternates between male and female names for each hurricane season. These names are kept short and are picked so they can be easily understood when communicating with the many agencies and groups in times of emergency. If a hurricane is so deadly or costly then the name is retired from the name databank.

Hurricane Katrina, which occurred in September of 2005, became the most costly natural disaster to hit the United Staes. In economic terms, it will cost hundreds of billions of dollars to rebuild the city of New Orleans and other areas of the Gulf coast. Environmental damage and social costs are much more difficult to measure and are impossible to put a dollar figure to them. Although Katrina weakened to a Category 3 hurricane at landfall near New Orleans, it overwhelmed the local dykes and storm barriers, flooding 80 % of the city. Almost 2000 people lost their lives and it will take years to rebuild New Orleans. Many former residents of this historic city refuse to move back due to the risk of future hurricanes.
Hurricane Katrina 
Courtesy of the NOAA


  1. National Hurricane Center
  2. Canadian Hurricane Centre


Although hurricanes are the largest storms on earth and cover huge areas, tornadoes are much smaller but can have higher wind speeds. Tornadoes can come in many shapes, but are typically in the form of a visible funnel, with the narrow end touching the earth. Often, a cloud of debris encircles the lower portion of the funnel. The base of the funnel appears dark because of the density of condensing moisture, dust, and debris swept up by the wind. Wind speeds in a tornado are greater than in any other storm. Most have winds of 75 km/h or less, are approximately 75 meters across, and travel several kilometres before dissipating. However, in rare cases, some tornadoes can have winds of more than 480 km/h, be over 1.6 km across, and stay on the ground for more than 100 kilometres. Tornadoes are mid-latitude storms that usually form over land where warm air from the Gulf of Mexico meets cool, dry air from Canada. Combined with upper level air flowing east over the Rocky Mountains into central United States is an area known as tornado alley, centred in Oklahoma and Kansas. Scientists continue to study how tornadoes form in an attempt to predict and track their movements. Two conditions are needed for the formation of a funnel cloud. First, there must be strong convection currents due to ground heating up. This causes cumulonimbus clouds to form with large amounts of moisture and energy. Secondly, a cold front must move into the area. This causes rising, hot, unstable air to be hit with a cold front moving in, usually from a southwest direction. When this occurs, the difference in the atmospheric pressure triggers the swirling funnel cloud. In order to measure the wind intensities and damage done by tornadoes, the Fujita scale rates each tornado on a scale from F0 to F5, with F0 being the least damaging while F5 is devastating to structures. Luckily, the vast majority of tornadoes in the world are F0 or F1, considered weak by tornado standards.

The following interactive simulation will allow you to view the damage caused by differing levels of tornadoes according to the Fujita Scale, begin here .