Overview Thunderstorm HazardsLightningProduced by every thunderstormHailFloodingStrong windsTornadoesLighteningLightning is an electrical discharge in the atmosphereThere are about 20 million cloud-to-ground lightning strokes per year in the United States aloneLightning kills about 50 people each year and injures around 300 (84% are male)Lightning causes $4-5 billion in damage per yearForest firesLightning StrokeLightning bolt is only about 1 inch (2-3 cm) wideBolt is about 3 miles (5 km) longTemperature: 30,000 oC (54,000 oF)Surface of sun: 6,000 oC (10,000 oF)Bolt can travel downward at over 100,000 mphCharge Separation in a CloudOpposite charges attract!Ice particles of different sizes collide in cloud and transfer electrical chargesLike dragging your socks across carpetLarge ice particles become negatively charged, fall downwardSmall ice particles become positively charged and stay higher in cloudEach collision transfers a small charge, but this occurs billions of times in a single stormBillions of small charges add up to a large charge!Types of LightningCloud-to-ground (CG)Only 20% of all lightning strokesCloud-to-cloud (CC)Intra-cloud (IC)Cloud-to-airSheet LighteningYou can see lightning from a long distance, especially at nightLight can be scattered by clouds and rain, resulting in sheet lightningEntire sky appears to light upMay not hear thunder because it is so far awaySometimes, this is mispronounced as “heat lightning” because it most frequently occurs on hot/humid nightsIf the heat truly caused the lightning, it would be so hot, you would be long dead!Your book is WRONG!!Lightning and ThunderLightning heats air around it, causing the air to expand violently, forming a sound waveTemperature can reach 30,000 oC (54,000 oF)About six times hotter than surface of sunWe hear this sound as thunderLight travels much faster than soundIt takes sound 5 seconds to travel 1 mileIf you can HEAR thunder, you are in danger of being struck by lightningLightning SafetyDuring a lighting storm, DON’TTake a showerUse a corded phoneIf outside, AVOIDOpen fieldsTreesMetal objectsWaterCrouch on ground in low spot if you cannot get insideMinimize contact with groundGet indoors or into a car if possibleHailHail is frozen precipitation that falls from thunderstormsHail is generally larger than 3 mm and can be up to grapefruit sizedMost hail is small (pea sized)Small hail can accumulate much like snow and sleetLarge hail requires strong updrafts, and hence supercell thunderstormsLargest hail falls closest to updraftHardness of hailstones variesCan be as soft as a snowball or rock hard!How to get big hail?Strong updraft (big CAPE)Cooler temperatures (less melting on the way down)Hail layersThis is NOT the result of hailstones making several trips up and down within a thunderstorm!!Wet growth = CLEAR ICEDry growth = CLOUDY ICEFlood StatisticsFloods kill more people worldwide than any other natural disaster (except droughts)Individual floods can cause billions of dollars in damage and can kill over 10,000 peopleCommon trait: Slow moving weather system that dumps a lot of rain over a particular regionFlood types:Flash floodsOccur rapidly, typically with little warningLocalized, short duration floodsGenerally less than 6 hoursUsually caused by slow-moving thunderstormsMesoscale convective systemsCan result in many injuries, fatalitiesWidespread floodsCover large areasDue to widespread heavy rains over several days or snowmeltAble to be forecast days in advanceFewer causalities, much greater damageFlood SafetyOnly 6 inches of flowing water can sweep you off of your feet!Never drive through flooded roadwaysA lot of flood-related fatalities occur in automobiles“Turn around, don’t drown”Get to higher ground!In the case of widespread flooding, follow directions and evacuationsThunderstorm Hazards 12/03/2012Overview Thunderstorm Hazards-LightningoProduced by every thunderstorm-Hail-Flooding-Strong winds-TornadoesLightening-Lightning is an electrical discharge in the atmosphere-There are about 20 million cloud-to-ground lightning strokes per year in the United States alone-Lightning kills about 50 people each year and injures around 300 (84% aremale)-Lightning causes $4-5 billion in damage per yearoForest fires-Lightning StrokeoLightning bolt is only about 1 inch (2-3 cm) wideoBolt is about 3 miles (5 km) longoTemperature: 30,000 oC (54,000 oF)Surface of sun: 6,000 oC (10,000 oF)oBolt can travel downward at over 100,000 mph-Charge Separation in a CloudoOpposite charges attract!oIce particles of different sizes collide in cloud and transfer electrical chargesLike dragging your socks across carpetoLarge ice particles become negatively charged, fall downwardoSmall ice particles become positively charged and stay higher in cloudoEach collision transfers a small charge, but this occurs billions of times in a single stormBillions of small charges add up to a large charge!-Types of LightningoCloud-to-ground (CG)Only 20% of all lightning strokesoCloud-to-cloud (CC)oIntra-cloud (IC)oCloud-to-airoSheet LighteningYou can see lightning from a long distance, especially at nightLight can be scattered by clouds and rain, resulting in sheet lightningEntire sky appears to light upMay not hear thunder because it is so far awaySometimes, this is mispronounced as “heat lightning” because it most frequently occurs on hot/humid nightsIf the heat truly caused the lightning, it would be so hot, you would be long dead!Your book is WRONG!!-Lightning and ThunderoLightning heats air around it, causing the air to expand violently, forming a sound waveTemperature can reach 30,000 oC (54,000 oF)About six times hotter than surface of sunoWe hear this sound as thunderoLight travels much faster than soundIt takes sound 5 seconds to travel 1 mileoIf you can HEAR thunder, you are in danger of being struck by lightning-Lightning SafetyoDuring a lighting storm, DON’TTake a showerUse a corded phoneoIf outside, AVOIDOpen fieldsTreesMetal objectsWateroCrouch on ground in low spot if you cannot get insideMinimize contact with groundoGet indoors or into a car if possibleHail-Hail is frozen precipitation that falls from thunderstormsoHail is generally larger than 3 mm and can be up to grapefruit sizedoMost hail is small (pea sized)oSmall hail can accumulate much like snow and sleet-Large hail requires strong updrafts, and