UIUC ATMS 100 - Thunderstorm Hazards (5 pages)

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Thunderstorm Hazards

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Thunderstorm Hazards


Brief overview of Thunderstorm Hazards: lightning, thunder, hail, and floods

Lecture number:
Lecture Note
University of Illinois at Urbana, Champaign
Atms 100 - Introduction to Meteorology
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Lecture 23 Outline of Last Lecture I What is a Downburst II Downburst Formation III Straight Line Winds IV Wind Damage V Mesoscale Convective VI MCS Lifecycle VII Stratiform Precipiation VIII MCS Dissipation IX MCS Structure X MCS Structure Updraf XI MCS Structure Rear Inflow Jet XII Vertical Wind Shear XIII The Role of Wind Shear XIV Shelf Cloud XV Bow Echoes ATMS 100 1st Edition Outline of Current Lecture XVI Thunderstorm Hazards XVII What is Lightning XVIII Lightning Bolt XIX Charge Separation XX Types of Lightning XXI Cloud to Ground Lightning XXII Sheet Lightning XXIII Lightning Stroke XXIV Lightning and Thunder XXV Positive Polarity Stroke XXVI Lightning Safety XXVII What is Hail XXVIII Lage Hail Hail XXIX Hail Layers XXX Flood Statistics XXXI Types of Floods XXXII Flash Floods XXXIII Widespread Floods XXXIV Flood Safety Current Lecture XXXV Thunderstorm Hazards a Lightning i produced by every thunderstorm b Hail c Flooding d Strong Winds i already discussed e Tornadoes XXXVI What is Lightning a lightning is an electrical discharge in the atmosphere b there are about 20 million cloud to ground lightning strokes per year in the United States alone c Lightning kills about 50 people each year and injures arund 300 84 are male d Lightning causes 4 5 billion in damage per year i forest fires XXXVII Lightning Bolt a lightning bolt is only about 1 inch 2 3 cm wide b bolt is about 3 miles 5 km long c Temperature 30 000 C i surface sun is 6 000 C d Bolt can travel downward at over 100 000 mph e Separation of electrical charges in cumulonimbus clouds key to lightning formation XXXVIII Charge Separation a opposite charges attract b ice particles of different sizes collide in cloud and transfer electrical charges i like dragging socks across carpet c large ice particles d small ice particles become positively charged and stay higher in cloud e each collision transfers a small charge but this occurs billions of times in single storm i billions of small charges add up to large charge XXXIX Types of Lightning a cloud to ground CG i only 20 of all lightning strokes b cloud to cloud CC c intra cloud IC d cloud to air CA XL Cloud to Ground Lightning XLI Sheet Lightning a you can see lightning from a long distance especially at night b light can be scattered by clouds and rain resulting in sheet lightning i entire sky appears to light up ii may not hear thunder because it is so far away c sometimes this is mispronounced as heat lighting because it is most frequently occurs on hot humid nights if the heat truly caused the lighting it would be so hot you would be dead ii your book is wrong XLII Lightning Stroke XLIII Lightning and Thunder a lightning heats air around it causing the air to expand violently forming a sound wave i temperature can reach 30 000 C ii about six times hotter than the surface of the sun b we hear this sound as thunder c light travels much faster than sound i it takes 5 seconds to travel 1 mile d if you can hear thunder you are in danger of being struck by lightning XLIV Positive Polarity Stroke XLV Lightning Safety a during a lightning storm DON T i take a shower ii used a corded phone b if outside AVOID i open fields ii trees iii metal objects iv water c crouch on the ground in low spot if you cannot get inside i minimize contact with ground d get indoors or into a car if possible XLVI What is Hail a Hail is frozen precipitation that falls from thunderstorms i hail is generally larger than 3 mm and can be up grapefruit sized ii most hail is small pea sized iii small hail can accumlate much like snow and sleet b large hail requires strong updrafs and hence supercell thunderstorms XLVII Large Hail Hail a Vivian SD July 23rd 2010 i diameters 8 inches circumference 18 62 inches weight 1 94 pounds ii requires updraf speed of around 180 mph b Oklahoma CIty OK May 16 c largest hail falls closest to updraf d hardness of hailstones varies i can be as sof as a snowball or rock hard e how to get big hail i strong updraf big CAPE ii cooler temperatures less melting on way down XLVIII Hail Layers i a this is not the result of hailstones making several trips up and down within a thunderstorm i wet growth clear ice ii dry growth cloudy ice XLIX Flood Statistics a floods kill more people worldwide than any other natural disaster except droughts b individual floods can cause billions of dollars in damage and can kill over 10 000 people c common trait slow moving weather system that dumps a lot of rain over a particular region L Types of Floods a flash floods b widspread floods LI Flash Floods a occur rapidly typically with little warning b localized short duration floods i generally less than 6 hours c usually caused by slow moving thunderstorms i mesoscale convective systems d can result in many injuries fatalities e examples i johnstown PA 1889 1936 1977 ii big thompson canyon CO 1976 iii Colorado september 2013 f thundersotmrs produce heavy rain that can lead to flooding g water is powerful i 6 inches of flowing water can wash you away ii 2 feet of flowing water can wash away a car iii nearly half of all flood fatalities occur in cars h floods kill an average of 127 people in the US each year i lightning 73 ii tornadoes 68 iii hurricanes 16 LII Widespread Floods a cover large areas b due to widepsread heavy rains over several days or snowmelt c able to be forecast days in advance d fewer causalities much greater damage e MS IL rivers APril 2013 LIII Flood Safety a only 6 inches of flowing water can sweep you off your feet b never drive through flooded roadways i a lot of flood related fatalities occur in cars c get to higher ground d in the case of widespread flooding follow directions and evacuations e water is POWERFUL

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