Lecture 23Outline of Last Lecture I. What is a Downburst?II. Downburst FormationIII. Straight Line WindsIV. Wind DamageV. Mesoscale ConvectiveVI. MCS LifecycleVII. Stratiform PrecipiationVIII.MCS DissipationIX. MCS StructureX. MCS Structure: UpdrafXI. MCS Structure: Rear Inflow JetXII. Vertical Wind ShearXIII. The Role of Wind ShearXIV. Shelf CloudXV. Bow EchoesATMS 100 1st EditionOutline of Current Lecture XVI. Thunderstorm HazardsXVII. What is Lightning?XVIII. Lightning BoltXIX.Charge SeparationXX. Types of LightningXXI.Cloud to Ground LightningXXII. Sheet LightningXXIII. Lightning StrokeXXIV. Lightning and ThunderXXV. Positive Polarity StrokeXXVI. Lightning SafetyXXVII. What is Hail?XXVIII. Lage Hail/HailXXIX. Hail LayersXXX. Flood StatisticsXXXI. Types of FloodsXXXII. Flash FloodsXXXIII. Widespread FloodsXXXIV. Flood SafetyCurrent LectureXXXV. Thunderstorm Hazardsa. Lightningi. produced by every thunderstormb. Hailc. Floodingd. Strong Windsi. already discussede. TornadoesXXXVI. What is Lightning?a. lightning is an electrical discharge in the atmosphereb. there are about 20 million cloud to ground lightning strokes per year in the United States alonec. Lightning kills about 50 people each year and injures arund 300 (84% are male)d. Lightning causes $4-5 billion in damage per yeari. forest firesXXXVII. Lightning Bolta. lightning bolt is only about 1 inch (2-3 cm) wideb. bolt is about 3 miles (5 km) longc. Temperature: 30,000 Ci. surface sun is 6,000 Cd. Bolt can travel downward at over 100,000 mphe. Separation of electrical charges in cumulonimbus clouds key to lightning formationXXXVIII. Charge Separationa. opposite charges attractb. ice particles of different sizes collide in cloud and transfer electrical chargesi. like dragging socks across carpetc. large ice particlesd. small ice particles become positively charged and stay higher in cloude. each collision transfers a small charge but this occurs billions of times in single stormi. billions of small charges add up to large chargeXXXIX. Types of Lightninga. cloud-to ground (CG)i. only 20% of all lightning strokesb. cloud-to-cloud (CC)c. intra-cloud (IC)d. cloud-to-air (CA)XL. Cloud to Ground LightningXLI. Sheet Lightninga. you can see lightning from a long distance, especially at nightb. light can be scattered by clouds and rain, resulting in sheet lightningi. entire sky appears to light upii. may not hear thunder because it is so far awayc. sometimes this is mispronounced as heat lighting because it is most frequently occurs on hot/humid nightsi. if the heat truly caused the lighting, it would be so hot, you would be deadii. your book is wrongXLII. Lightning StrokeXLIII. Lightning and Thundera. lightning heats air around it, causing the air to expand violently forming a sound wavei. temperature can reach 30,000 Cii. about six times hotter than the surface of the sunb. we hear this sound as thunderc. light travels much faster than soundi. it takes 5 seconds to travel 1 miled. if you can hear thunder, you are in danger of being struck by lightningXLIV. Positive Polarity StrokeXLV.Lightning Safetya. during a lightning storm DON’T:i. take a showerii. used a corded phoneb. if outside, AVOID:i. open fieldsii. treesiii. metal objectsiv. waterc. crouch on the ground in low spot if you cannot get insidei. minimize contact with groundd. get indoors or into a car if possibleXLVI. What is Hail?a. Hail is frozen precipitation that falls from thunderstormsi. hail is generally larger than 3 mm and can be up grapefruit sizedii. most hail is small (pea sized)iii. small hail can accumlate much like snow and sleetb. large hail requires strong updrafs, and hence supercell thunderstormsXLVII. Large Hail/Haila. Vivian, SD July 23rd 2010i. diameters 8 inches, circumference 18.62 inches, weight 1.94 poundsii. requires updraf speed of around 180 mphb. Oklahoma CIty, OK May 16c. largest hail falls closest to updrafd. hardness of hailstones variesi. can be as sof as a snowball or rock harde. how to get big hail?i. strong updraf (big CAPE)ii. cooler temperatures (less melting on way down)XLVIII. Hail Layersa. this is not the result of hailstones making several trips up and down within a thunderstormi. wet growth= clear iceii. dry growth= cloudy iceXLIX. Flood Statisticsa. 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 peoplec. common trait: slow moving weather system that dumps a lot of rain over a particular regionL. Types of Floodsa. flash floodsb. widspread floodsLI. Flash Floodsa. occur rapidly, typically with little warningb. localized, short duration floodsi. generally less than 6 hoursc. usually caused by slow moving thunderstormsi. mesoscale convective systemsd. can result in many injuries, fatalitiese. examplesi. johnstown, PA (1889, 1936, 1977)ii. big thompson canyon, CO (1976)iii. Colorado (september 2013)f. thundersotmrs produce heavy rain that can lead to floodingg. water is powerfuli. 6 inches of flowing water can wash you awayii. 2 feet of flowing water can wash away a cariii. nearly half of all flood fatalities occur in carsh. floods kill an average of 127 people in the US each yeari. lightning: 73ii. tornadoes: 68iii. hurricanes: 16LII. Widespread Floodsa. cover large areasb. due to widepsread heavy rains over several days or snowmeltc. able to be forecast days in advanced. fewer causalities much greater damagee. MS/IL rivers, APril 2013LIII. Flood Safetya. only 6 inches of flowing water can sweep you off your feet b. never drive through flooded roadwaysi. a lot of flood related fatalities occur in carsc. get to higher groundd. in the case of widespread flooding, follow directions and evacuationse. water is