Severe WeatherSevere Weather

SWBAT explain why some thunderstorms are SWBAT explain why some thunderstorms are more severe than others; recognize the more severe than others; recognize the

dangers of severe thunderstorms; describe dangers of severe thunderstorms; describe how tornadoes formhow tornadoes form

Severe ThunderstormsSevere Thunderstorms

Why are some thunderstorms more severe Why are some thunderstorms more severe than other?than other? An increased temperature difference between An increased temperature difference between

the upper and lower parts of the storm can the upper and lower parts of the storm can cause the air to be more unstable. The cause the air to be more unstable. The greater the instability the more severe the greater the instability the more severe the storm is, due to the increased up and down storm is, due to the increased up and down drafts.drafts.

Severe ThunderstormsSevere Thunderstorms

SupercellSupercell Self-sustaining, extremely powerful storms Self-sustaining, extremely powerful storms

that are characterized by intense, rotating that are characterized by intense, rotating updraftsupdrafts

Dangers Associated with Dangers Associated with ThunderstormsThunderstorms

LightningLightning Electricity caused by the rapid rush of air in a Electricity caused by the rapid rush of air in a

cumulonimbus cloud.cumulonimbus cloud. A bolt forms when friction between the updrafts and A bolt forms when friction between the updrafts and

downdrafts separate electrons from some of the downdrafts separate electrons from some of the atoms creating positively charged ions and regions of atoms creating positively charged ions and regions of opposite charge.opposite charge.

To relieve the imbalance a channel of negatively To relieve the imbalance a channel of negatively charged air moves from the cloud to the ground charged air moves from the cloud to the ground causing a positively charged ion channel to surge causing a positively charged ion channel to surge back up from the ground, channeling about 100 back up from the ground, channeling about 100 million volts of electricity.million volts of electricity.

Dangers Associated with Dangers Associated with ThunderstormsThunderstorms

WindWind Sometimes the downdrafts are not dispersed Sometimes the downdrafts are not dispersed

and are concentrated in downbursts. and are concentrated in downbursts. They travel between 200 and 250 km/hr They travel between 200 and 250 km/hr

(approximately 125-155 mph) and can be (approximately 125-155 mph) and can be deadly even though they don’t last long.deadly even though they don’t last long.

Dangers Associated with Dangers Associated with ThunderstormsThunderstorms

HailHail Precipitation in the form of lumps of ice.Precipitation in the form of lumps of ice. It can cause tremendous damage (almost $1 It can cause tremendous damage (almost $1

billion a year).billion a year). It’s most common during the spring.It’s most common during the spring. If caught in a convection current hail can grow If caught in a convection current hail can grow

quite large before they fall.quite large before they fall.

Dangers Associated with Dangers Associated with ThunderstormsThunderstorms

FloodsFloods Slower moving storms dump more rain over a Slower moving storms dump more rain over a

limited location, rather than spreading it out. limited location, rather than spreading it out. If there is abundant moisture in the area it is If there is abundant moisture in the area it is

easier to cause flooding.easier to cause flooding. Floods are the main cause of thunderstorms Floods are the main cause of thunderstorms

related deaths in the US each year.related deaths in the US each year.

Dangers Associated with Dangers Associated with ThunderstormsThunderstorms

TornadosTornados Violent, whirling column of air in contact with Violent, whirling column of air in contact with

the ground (funnel cloud).the ground (funnel cloud). These are associated with the most severe These are associated with the most severe

thunderstorms.thunderstorms. They form when wind speed and direction They form when wind speed and direction

change suddenly with height, known as a change suddenly with height, known as a wind shear.wind shear.

If the rotation takes place near an updraft it If the rotation takes place near an updraft it can tilted vertically.can tilted vertically.

Severe WeatherSevere Weather

DownburstsDownbursts Violent downdrafts that are concentrated in a Violent downdrafts that are concentrated in a

local arealocal area Fujita tornado intensity scaleFujita tornado intensity scale

A rank is given according to a tornados path A rank is given according to a tornados path of destruction, wind speed, and durationof destruction, wind speed, and duration

With a partnerWith a partner

Answer assessment questions 1-6, on Answer assessment questions 1-6, on page 340page 340

Be sure to answer in complete sentences.Be sure to answer in complete sentences. Finish for homework.Finish for homework.