Weather

1. Weather Part 6: Storms

2. What Is a Storm? • A violent disturbance in the atmosphere • Marked by sudden changes in air pressure and high winds • May cover a large or small area

3. Rainstorms and Snowstorms • Happen when two different fronts collide • When a warm front meets a cold front nimbostratus clouds form • Precipitation falls as rain if it is warm and as snow if it is cold http://www.flickr.com/photos/24841050@N00/2684722

4. Ice Storm • When heavy rain falling over a wide area freezes on contact, resulting in a layer of ice coating everything • Can cause great damage by knocking down trees and power lines

5. Blizzard • A severe snowstorm with sustained wind speeds, or frequent gusts, greater than 56 km/h (35 mph), that lasts for 3 or more hours • May be accompanied by severe cold and large amounts of drifting snow 'Description:''' Standing tall on North Dakota snow A March blizzard nearly buried utility poles. Caption jokingly read "I believe there is a train under here somewhere!" *'''Source:''' http://www.photolib.noaa.gov/historic/nws/wea00958.htm*'''Image I

6. Thunderstorms • Heavy rainstorms accompanied by thunder and lightning • May also have violent downdrafts and wind shear (a great change in wind speed over a short distance) that are hazards for planes • Occur when a cold front moves in and meets a warm front causing the formation of cumulonimbus clouds

7. Thunderstorms Lightning occurs when areas of positive and negative electric charges build up in the storm clouds and discharge suddenly License:Some rights reserved by BobyDimitrov

8. Thunderstorms Thunder occurs because the lightning superheats the air causing it to expand rapidly and create sound waves. License:Some rights reserved by BobyDimitrov

9. Thunderstorms Since light travels much faster than sound, there is about a 5 seconds per mile delay between seeing the lightning and hearing the thunder, or 3 s/km. License:Some rights reserved by BobyDimitrov

10. Thunderstorms • Lightning striking the ground is the leading cause of forest fires in the western states. • More people are killed by lightning than by any other type of violent storm. License:Some rights reserved by BobyDimitrov

11. Thunderstorm Safety FYI • Seek shelter before an approaching thunderstorm - Lightning can strike as far as 10 miles away from where it is raining. That’s about the distance you can hear thunder. If you can hear thunder, you are within striking distance. Seek shelter immediately! Get inside a home, large building, or an all-metal (not convertible) automobile. When thunder roars, go indoors! • Do not stand underneath a natural lightning rod such as a tall, isolated tree or a telephone pole. • Avoid projecting above the surrounding landscape; for example, do not stand on a hilltop. • In a forest, seek shelter in a low area under a thick growth of small trees. In open areas, go to a low place such as a ravine or valley.

12. Thunderstorm Safety FYI • Get away from open water, tractors and other metal farm equipment, and small metal vehicles such as motorcycles, bicycles, and golf carts. • Avoid metal including wire fences, clotheslines, metal pipes and rails; put down golf clubs. • Things to avoid while indoors - While inside, stay off land lines or corded phones, computers and other electrical equipment that put you in direct contact with electricity. Stay away from indoor and outdoor pools, bathtubs, showers, and other plumbing. When inside, wait 30 minutes after the last sound of thunder and lightning before going out again. • Safe Shelter from Storms - A house or other substantial building offers the best protection from lightning. For a shelter to provide adequate protection from lightning, it must contain a mechanism for conducting the electrical current from the point of contact to the ground (ie. wiring, plumbing, metal gutters and downspouts, etc.).

13. Thunderstorm Safety FYI • Unsafe Sheltering - Unless specifically designed to be lightning safe, small structures do little, if anything to protect people from lightning. A shelter that does not contain plumbing or wiring throughout, or some other mechanism for grounding from the roof to the ground is not safe. Small wooden, vinyl or metal sheds offer little or no protection from lightning and should be avoided during thunderstorms. • Protect Your Pets - Outside dog houses are not lightning-safe. Dogs that are chained to trees or wire runners can easily fall victim to lightning strikes. Consider bringing your pets inside the home or garage during thunderstorms. • Finally, if you are caught out in a level field or in the open, away from shelter, and you feel your hair stand on end, lightning may be about to strike you. Drop to your knees and bend forward, putting your hands on your knees. Do not lie flat on the ground. Sources: http://www.crh.noaa.gov/lmk/?n=weathersafetyrules http://www.weathersafety.ohio.gov/thunderstormsandlightningsafety.aspx

14. Cyclones • Cyclones form around areas of low pressure • Contain rising warm air • Winds spiral around and into the center in a counterclockwise direction in the Northern Hemisphere, due to the _________. • Usually cause rainy, stormy weather Original caption from NASA: "A beautifully-formed low-pressure system swirls off the southwestern coast of Iceland, illustrating the maxim that "nature abhors a vacuum." The vacuum in this case would be a region of low atmospheric pressure. In order to fill this void, air from a nearby high-pressure system moves in, in this case bringing clouds along for the ride….”

15. Anticyclones • High pressure areas • Winds spiral around and out from center, clockwise in the Northern Hemisphere • Weather is usually clear, dry, and fair. A Unusual Anticyclone in Southern Australia. Satellite loop at the time the image above was taken, showed the Anticyclone was spinning counterclockwise, as it is in the Southern Hemisphere. 

16. Hurricanes • A type of tropical cyclone • A tropical cyclone is a low pressure system with an organized circulation that develops over the tropical or subtropical waters. Tropical Cyclones have different names depending on where they form: • Hurricanes - Atlantic and Eastern Pacific oceans • Typhoons -Western Pacific • Cyclones – Indian ocean

17. Hurricanes • Definition: An intense tropical weather system with a well defined circulation and maximum sustained winds of 74 mph (64 knots) or higher. • Powered by heat from the sea so require ocean temperatures of at least 80ºF or 27ºC to form • Eye: center of the hurricane where winds are calm • Hurricane damage is caused by high winds and large amounts of rain. • Storm surge:water is pushed toward the shore by the force of the storm winds, which can cause hurricane storm tides with a mean water level 15 feet or more above normal, and then wind driven waves are superimposed on the storm tide.  • Coastal damage can be particularly severe due to storm surge

18. Hurricane Categories • Saffir/Simpson Hurricane Scale • 5 categories based primarily on wind speeds • Scale includes estimates for associated storm surge and barometric pressure for each level Categories (wind speeds): • 1 – Minimal (74-95 mph) • 2 – Moderate (96-110 mph) • 3 – Extensive (111-120 mph) • 4 – Extreme (130 – 156 mph) • 5 – Catastrophic (157 mph or higher) See animation at http://www.nhc.noaa.gov/aboutsshws.php

19. Hurricanes • Read about how hurricanes are named at http://www.nhc.noaa.gov/aboutnames.shtml • Hurricane Hunters video: http://oceantoday.noaa.gov/hurricanehunters/ • The 2012 Atlantic Hurricane Season in 4.5 Minutes • Formation of a Hurricane • Hurricanes are the most powerful storms on Earth in terms of total energy involved.

20. Tornadoes • A narrow, violently rotating column of air that extends from the base of a thunderstorm to the ground. • Becomes visible whenit forms a condensation funnel made up of water droplets, dust and debris. • Most violent of all atmospheric storms.

21. Tornadoes • The strength of a tornado is accessed after the fact by the amount of damage it caused. • Enhanced F-scale rates tornadoes as F0 to F5 • Wind speed can only be directly measured for the weakest of tornadoes. • The highest speed ever remotely measured was 302 mph, the highest wind speed ever detected near the Earth’s surface.

22. Tornado Alley • “Tornado Alley is a nickname in the popular media for a broad swath of relatively high tornado occurrence in the central U. S. • Violent or killer tornadoes do happen outside this Tornado Alley every year. • Tornadoes can occur almost anywhere in the U. S., including west of the Rockies and east of the Appalachians.” Source: http://www.spc.noaa.gov/faq/tornado/

23. Tornadoes • Video:http://www.youtube.com/watch?feature=player_embedded&v=43VoMesUd2Q • Read Tornado Facts at http://www.sciencekids.co.nz/sciencefacts/weather/tornado.html