Weather Definitions to
be used in the PowerPoint

**Note dewpoint has been moved. It now follows psychrometer and comes
before atmospheric pressure as it is related to humidity in the air.
 

The first eight points deal with severe weather. It is probably easier to dedicate two pages to each weather event. On the first give the definition of the conditions that define that weather event and on the second describe the where and when of that severe weather event occurrence in Canada along with three 'interesting facts' about that event.   1. A tornado is a vortex of rapidly moving air associated with a thunderstorm 2. A Hurricane is a severe tropical cyclone usually with heavy rains and winds moving a 73-136 knots (12 on the Beaufort scale) A cyclone is a low pressure, air mass that is rotating inward (counter clockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere). 3. A blizzard is a severe storm with strong winds (greater than 40 km/h), low temperatures, and blowing snow that reduces visibility to 1 km or less and that lasts for at least three hours. 4. A hail storm is Any storm that produces hailstones that fall to the ground; usually used when the amount or size of the hail is considered significant. 5. A thunderstorm is a severe storm several kilometres in diameter created by the rapid lifting of moist warm air which creates a cumulonimbus cloud and which may include lightning, thunder, heavy rain, or hail. 6. A flood is excess water from rain, rivers, or oceans that cannot be absorbed by the surrounding land. 7. An ice storm is where falling rain freezes instantly when coming in contact with a surface, forming a coat of ice on the surface. 8. A drought is a period in which the rainfall for an area is much less than average.   The next four points deal with scales. Search the internet for graphics that explain how the scale works. Remember though that this is a PowerPoint presentation, so the graphic must be legible. If the text is too small the graphic will not add to your presentation.   1. A Beaufort Wind Scale is a scale classifying wind strength in terms of observable effects on the sea and over land. 2. A Saffir-Simpson hurricane scale divides hurricanes into five categories based on the storm's wind speed. It does not include wind gusts but sustained wind speed. 3. The Humidex is a pseudo "temperature" that does not tell us how hot the day is but rather how hot the day feels due to the relative humidity. 4. The UV index identifies how strong the ultraviolet (UV) radiation is from the sun.   The next five points deal with humidity. For Hygrometer and Psychrometer find a picture on Google images and find out how the two are related.   1. Humidity is the amount of water vapour in a sample of air. 2. Relative humidity is the percentage of water the air is holding compared to the maximum amount of water the air could hold at that temperature. 3. Hygrometer is a device used to measure the atmospheric humidity. 4. Psychrometer is a device used to measure the atmospheric humidity. 5. As air cools it is able to hold less and less moisture. The dew point is the temperature the air around us can be cooled to before it would be completely saturated. If cooled anymore precipitation would begin to form.   The next two points deal with Pressure. The exploration of how to measure atmospheric pressure may consist of two or more pages depending on how many different ways you find to measure atmospheric pressure. Be sure to include graphics and explanations how the atmospheric pressure is measured in each method.   1. Atmospheric pressure is also known as barometric pressure. It is the pressure exerted on us due to the weight of all the air in the atmosphere over us. The higher we are from sea level the less atmospheric pressure there is as there is less atmosphere above us. 2. Explore the Internet to determine how atmospheric pressure is measured.   The final seven points deal with the definition of precipitation and the different forms that we experience here on Earth.   1. Precipitation is water that falls to the ground in liquid or solid form. 2. Rain is falling water droplets that have a diameter between 0.5 mm and 5 mm. 3. Drizzle is falling water droplets that have a diameter between .040 mm and 0.5 mm. 4. Sleet is ice pellets (frozen raindrops) that bounce upon impact with the ground. 5. Snow is frozen water crystals that form below 0°C. 6. Fog is low flying cloud that has water droplets or ice crystals that reduce visibility on the Earth's surface to less than 1 km. 7. Hail is frozen water droplets that are created by cycling through highly active thunderclouds many times.