1. Severe Weather

2. Watch Vs. Warning Watch= The conditions are right for severe weather. –Stay tuned to reports Warning= Severe weather has been sighted and it is advised to take cover.

3. Thunderstorms Fast Facts: –Typically about 15 miles in Diameter –Last 30 minutes –Can occur at any moment around the world –16 Million Per Year –Severe Hail a ¾ of inch

4. How They Form Cumulonimbus clouds Caused by a cold front Also on hot, humid afternoons Three Key Ingredients –War Humid Air (Fuel) –Triggering mechanism What starts the storm Lifts moisture upwards so clouds can form and updrafts develop Instability –Allows updrafts to accelerate up and down at high rates

5. Lightening & Thunder Areas of positive and negative electrical charges build up in the storm clouds Lightening=energy discharge as the charges jump b/w parts of a cloud, nearby clouds, or clouds and the ground –Can heat to as much as 30,000 degrees Celcius –Hotter than the surface of the sun.

6. Lightening & Thunder Cont. Thunder, what causes it? –The rapid heating of the air which expands suddenly and expands. –Light Travels faster than sound.

7. Tornadoes A rapidly, whirling, funnel- shaped cloud that reaches down from the storm cloud to touch the Earth’s surface Form along front Not all reach the Earth –May touch for 15 minutes or less and be only a few 100 meters across Strength –Wind speeds can reach 500km/hr –Updraft in center is most powerful How they form –Low, heavy cumulonimbus clouds. –Spring and Early summer –In the afternoon or early evening. Build up of heat in lower atmosphere –Warm, Moist air mass from Gulf of Mexico (Maritime Tropical) meets with cold, dry mass from Canada (Continental Polar)

8. Tornadoes Cont. Where are they located? –Can occur anywhere, usually in spring and summer. –Most in world occur in U.S. About 700-800 a year –Tornado Alley Texas, Oklahoma, Kansas, Nebraska, Iowa Parts of Missouri, New Mexico, & South Dakota