RainPurple

=  SEVERE RAIN Hannah C and Michelle R = = Purple Class =

 Introduction﻿ Severe rain can present itself in many different ways but the most dangerous form is in severe thunderstorms. When there a re severe thunderstorms there is very heavy rain which lead to flash flooding. Flash flooding is when so much water accumulates on the ground to the point of saturation in a short amount of time, and as a consequence there is flooding. Thunderstorms can also cause strong winds, hail, lightening and even tornadoes. The average diameter of a thunderstorm cloud is 15m, and they typically last for about twenty to thirty minutes. There is an average of 100,000 thunderstorms in the US per day, 10% are classified as severe.(1)

Dangers ====Severe thunderstorms can cause tornadoes, hail at east 3/4 of an inch in diameter and strong winds blowing at the lowest speed of fifty eight miles per hour. Thunderstorms also cause lightning, which causes more deaths per year t hen both tornadoes and hurricanes. If struck by lightening there are also long-term effects if you survive including memory loss, problems paying attention, sleeping disorders, numbness, dizziness, stiffness in joints, fatigue, weakness, muscle spasms, depression and inability to sit for long spans of time. Hail can be a major problem and some can break glass, dent cars, harm your home, or seriously hurt people or animals if hit by it. The dangerously strong winds can reach up to a hundred to a hundred and fifty miles per hour, causing vehicles to flip, destroying homes, trees, utility poles, and anything caught in its path. Flooding can also be very harmful to an urban area. Floods have ruined homes, caused people to drown, block roads, damage farmland, and bring water-born disease.(2) ==== [|Click here to watch a video of an extreme lightening storm] Conditions of Formation What causes extreme thunderstorms to form? There are three ingredients needed to form a thunderstorm: moisture, instability, and lift. The developing stage of thunderstorms occurs when warm moist air rises into the cooler air above. As the warm air cools, condensation occurs forming clouds. Convection within the cloud continues the cloud to develop until it reaches the cumulonimbus stage. The cloud grows until it reaches the tropopause, and at this point ice crystals for due to the cold temperature, and when the condensation clings on to these ice crystals, we have rain. If updrafts of the warm air going through this process reaches the stratosphere then severe thunderstorms that are often tornadic occur. Downdrafts then occur due to the cooling of the air and the precipitation, and the two opposite drafts hitting each other is what causes lightening. (5)

Historical Examples ====﻿﻿On May 5th 1995 in Fort Worth, Texas, a severe thunderstorm struck an outdoor festival that had an attendance of more than 100,000. Softball sized hail struck the people injuring 100 people, shattered windows, and damaged cars. Winds reached up to 70 miles per house, destroying a GM plant and blowing over a RV park. The storm then moved to Dallas county and created record rainfall. Rain poured down at a rate of 3 inches per 30 minutes, causing massive flash flooding. Sixteen people died due to drowning, and a total of 20 people died due to the storm. Hundreds of homes, buisnesses and vehicles were destroyed, and the damage done cost billions of dollars. (3)====

[|Click here to watch a severe thunderstorm video]

 Safety For protection from this dangerous form of severe weather, you should take some safety precautions. If your in your home when a thunderstorm strikes it would be smart to secure objects outside of your home, stay inside during the storm, pull your car into your garage (to protect from hail) unplug electronics, stay off of the phone, stay out of the shower, and keep a distance from the windows. If you happen to be traveling during a thunderstorm one should stay in their vehicle, try to park under an overpass, stay away from open fields and tall trees, and stay away from bodies of water. One thing you can do to be aware of and lower the the risk of being struck by lightning is counting how many seconds there between a flash of lightning and a clap of thunder and divide that number by five. With that number you know how far away the storm is.(4)



Sources

Online Articles 1. "Severe Thunderstorms" Red Cross March 2007, November 21 2010 http://www.redcross.org/images/pdfs/code/thunderstorms.pdf

2. "Thunderstorms" National Disaster Education, Red Cross, November 22, 2010 http://www.etskywarn.net/skywarn/downloads/rcthunder.pdf

3. "Severe Thunderstorms" The Weather Channel, November 30, 2010 http://www.weather.com/encyclopedia/thunder/svrtstm.html

4. "Severe Thunderstorm Public Safety" Weather Prediction Education, December 2, 2010 http://www.theweatherprediction.com/wxsafety/storm/

Book Sources 5. Burroughs, J William. Weather. San Francisco: Time-Life Books 1996