THUNDERSTORMS, LIGHTNING and THUNDERSTORMS, LIGHTNING and

TORNADOESTORNADOES

pcooke 5/10/03

Thunderstorm Frequency

Average Days of Thunderstorms per Year

Thunderstorm FrequencyThunderstorm Frequency1500 to 2000 thunderstorms 1500 to 2000 thunderstorms occur around the world at any occur around the world at any

given momentgiven moment

FORMATION OF A CUMULONIMBUS

Thunderstorms are created Thunderstorms are created when large parcels of warm, when large parcels of warm, moist air rise into cooler airmoist air rise into cooler air

A cold front or convection A cold front or convection typically causes the warm air typically causes the warm air to rise and water vapor to to rise and water vapor to condense.condense.

All thunderstorms have 3 All thunderstorms have 3 stages:stages:

Ordinary ThunderstormsOrdinary Thunderstorms

• Ordinary Ordinary thunderstorms are not thunderstorms are not associated with fronts associated with fronts or severe or severe weather….they weather….they typically form on hot, typically form on hot, humid afternoons due humid afternoons due to convectionto convection

• These storms are like These storms are like mini-heat engines…mini-heat engines…they need warm, they need warm, moist air to keep them moist air to keep them alive…if that supply is alive…if that supply is cut off, the storm cut off, the storm dies :(dies :(

• TS Video

LLife cycle of an ordinary thunderstormife cycle of an ordinary thunderstorm

Cumulus stageCumulus stage Mature stageMature stage Dissipating stageDissipating stage

Cumulus Stage

As a cumulus cloud builds, As a cumulus cloud builds, water vapor condenses and water vapor condenses and releases heat which keeps the releases heat which keeps the rising air inside the cloud rising air inside the cloud warmer than environment.warmer than environment.

At this point, there is no time At this point, there is no time for precipitation to fall because for precipitation to fall because updrafts updrafts (which may reach (which may reach 100mph!!)100mph!!) keep water droplets keep water droplets and ice crystals suspended and ice crystals suspended within the cloudwithin the cloud

The building cumulus takes on The building cumulus takes on the appearance of a ‘tower’the appearance of a ‘tower’

Mature StageMature Stage

As the cloud builds higher As the cloud builds higher than the freezing level, cloud than the freezing level, cloud dropletsdroplets grow. Eventually, the rising grow. Eventually, the rising air can no longer keep the air can no longer keep the particles suspended and they particles suspended and they begin to fall. begin to fall.

Some raindrops evaporate on Some raindrops evaporate on the way down, which cools the way down, which cools the air. the air.

The cooler air begins to The cooler air begins to descend as a descend as a downdraftdowndraft..

The appearance of the The appearance of the downdraft marks the downdraft marks the beginning of the mature beginning of the mature stage.stage.

Mature ThunderstormsMature Thunderstorms

Large, mature Large, mature thunderstorms thunderstorms can…can…

• Produce precipitation at Produce precipitation at astonishing rates, up to 14 astonishing rates, up to 14 inches/hr. This causes local inches/hr. This causes local flooding.flooding.

• Create hailstones as large Create hailstones as large as grapefruits! Ouch!as grapefruits! Ouch!

• Generate tremendous Generate tremendous

electrical power and electrical power and intense lightning. intense lightning.

• Produce tornadoes with Produce tornadoes with devastating swirling windsdevastating swirling winds

Thunderstorm StructureThunderstorm Structure

updraft

Dissipating Stage

Occurs when updrafts Occurs when updrafts weaken and downdrafts weaken and downdrafts dominate throughout much dominate throughout much of the cloud.of the cloud.

The reason ordinary T-storms do not last very long is the downdrafts cut off the storm’s fuel supply by destroying the humid updrafts.

T-storms produce summer rainfall for a large portion of the US, and provide momentary cooling during a hot day.TS Formation

Severe and Supercell ThunderstormsSevere and Supercell Thunderstorms

Severe ThunderstormsSevere Thunderstorms

• If convection is strong If convection is strong and updrafts are and updrafts are intense, the storm can intense, the storm can become become severesevere..

• Updrafts in severe Updrafts in severe thunderstorms can thunderstorms can cause the cloud to cause the cloud to reach into the reach into the stratosphere and in stratosphere and in some cases extend up some cases extend up to 60,000 ft.to 60,000 ft.

• These storms contain These storms contain lightning, thunder, lightning, thunder, gusty winds, and hailgusty winds, and hail

Severe Thunderstorms• Strong updrafts can Strong updrafts can

keep hailstones keep hailstones suspended in the cloud suspended in the cloud long enough for them to long enough for them to grow to immense sizes! grow to immense sizes!

• Once they become large Once they become large enough they either fall enough they either fall out the bottom of the out the bottom of the cloud within a downdraft cloud within a downdraft or a strong updraft may or a strong updraft may toss them out the side. toss them out the side.

• Aircraft have Aircraft have encountered hail in clear encountered hail in clear air several miles away air several miles away from a storm.from a storm.

• Severe TS

The Supercell ThunderstormThe Supercell Thunderstorm• When winds become When winds become

stronger aloft, it causes stronger aloft, it causes the entire storm to the entire storm to rotate...rotate...

• ……and the thunderstorm and the thunderstorm may grow into a larger, may grow into a larger, long-lasting (longer than long-lasting (longer than an hour), severe storm an hour), severe storm called a called a Supercell.Supercell.

• The rotation of The rotation of supercells can lead to supercells can lead to the formation of the formation of tornadoes.tornadoes.

• Supercells

Rotating wall cloudRotating wall cloud

Extreme Low pressure Extreme Low pressure inside the Supercell inside the Supercell causes a lowering of causes a lowering of

the cloud base, called a the cloud base, called a Wall Cloud.Wall Cloud.

A A wall cloudwall cloud associated with a associated with a supercell supercell thunderstorm thunderstorm spins spins counterclockwisecounterclockwise

The first The first sign the sign the supercell supercell may form a may form a tornado is tornado is the the formation of formation of a a wall cloudwall cloud..

Supercell Miami Tornado

Fig. 10-4, p. 268

A supercell thunderstorm with a tornado sweeps over Texas

Fig. 10-11, p. 271

A dramatic example of a shelf cloud (or arcus cloud) associated with an intense thunderstorm

Mammatus clouds out ahead of a thunderstorm

Abrupt changes from moist to dry air, called drylines, form in Abrupt changes from moist to dry air, called drylines, form in western TX, OK, and KS in the spring and summer.western TX, OK, and KS in the spring and summer.

The diagram illustrates how cool “cP” air pushes hot and dry “cT” The diagram illustrates how cool “cP” air pushes hot and dry “cT” air over the warm moist “mT” air.air over the warm moist “mT” air.

This mixing of different air masses can create supercell storms.This mixing of different air masses can create supercell storms.

Conditions for SupercellsConditions for Supercells

Lightning and Thunder

Lightning may take place Lightning may take place within a cloud, from , from cloud to cloud, , from a cloud to surrounding air, from cloud to ground, or from a cloud to surrounding air, from cloud to ground, or

from from ground to cloud….only 20% strike the ground….only 20% strike the ground

Ball Lightning

A lightning stroke can heat the air to 30,000°C !!! This A lightning stroke can heat the air to 30,000°C !!! This extreme heating causes the air to expand explosively, extreme heating causes the air to expand explosively,

initiating a booming sound wave– called thunder.initiating a booming sound wave– called thunder.

Lightning occurs when positive and negative charges build up Lightning occurs when positive and negative charges build up in different regions of a cumulonimbusin different regions of a cumulonimbus cloud or between the cloud or between the

cloud and ground.cloud and ground.

Fig. 10-21, p. 279

The top of the cloud becomes positively charged.The top of the cloud becomes positively charged. The bottom The bottom of the cloud becomes negatively chargedof the cloud becomes negatively charged

The lightning stroke can travel in a number of directionsThe lightning stroke can travel in a number of directions

WWNotice that the cloud-toNotice that the cloud-to--ground lightning can travel out ground lightning can travel out away from the cloud, then turn downward, striking the away from the cloud, then turn downward, striking the

ground many miles from the thunderstorm. ground many miles from the thunderstorm.

A A cloud-to-groundcloud-to-ground lightning flash hitting a lightning flash hitting a 65-foot sycamore tree.65-foot sycamore tree.

It should be apparent It should be apparent why one should why one should notnot seek shelter under a seek shelter under a tree during a tree during a thunderstorm.thunderstorm.

6000 strikes per 6000 strikes per minute worldwide!minute worldwide!

Lightning is Lightning is responsible for responsible for more deaths more deaths annually than annually than tornadoes and tornadoes and hurricanes hurricanes combined.combined.

It causes fires and It causes fires and is often responsible is often responsible for urban blackoutsfor urban blackouts

Florida has the Florida has the most in the US. most in the US. Why?Why?

•The The 44 marks on the road represent areas where lightning, after striking marks on the road represent areas where lightning, after striking a cara car, , entered the roadway through the tires. entered the roadway through the tires.

•Lightning flattened Lightning flattened 33 of the car’s tires and damaged the radio antenna. of the car’s tires and damaged the radio antenna.

•The driver and a The driver and a 6 6 year-old were taken to a nearby hospital, treated for year-old were taken to a nearby hospital, treated for shock, and released.shock, and released.

Tornadoes

Tornadoes• A tornado is a rapidly A tornado is a rapidly

rotating column of air rotating column of air which rotates around a which rotates around a small area of intense low small area of intense low pressure and pressure and reaches the reaches the groundground

• A funnel cloud, is a A funnel cloud, is a tornado which has not tornado which has not reached the ground.reached the ground.

• Sometimes called Sometimes called twisterstwisters or or cyclonescyclones, tornadoes can , tornadoes can assume a variety of assume a variety of shapes and forms which shapes and forms which range from…..range from…..

Twisting-rope Twisting-rope tornadoes….ooooh!!tornadoes….ooooh!!

To Cylindrical Shaped To Cylindrical Shaped Tornadoes….aaahhhh!!Tornadoes….aaahhhh!!

Tornadoes

• A majority of North A majority of North American tornadoes American tornadoes rotate counterclockwise rotate counterclockwise about a central area of about a central area of low pressure. low pressure.

• The width of most The width of most tornadoes is between tornadoes is between 300-2000 ft., but some 300-2000 ft., but some are only….. are only…..

……while others…..while others…..

10 feet wide…10 feet wide…

Aww Aww how how cutecute

……have diameters exceeding 1 mile!....have diameters exceeding 1 mile!....

Like the Waco, TX Like the Waco, TX Tornado of Tornado of

1971….whoa!!!1971….whoa!!!

The Fujita ScaleThe Fujita Scale

• Winds in Winds in tornadoes are tornadoes are very very destructive….yadestructive….yah, no kidding….h, no kidding….

• Most have Most have winds which are winds which are 150mph or less, 150mph or less, but the most but the most powerful have powerful have winds up to winds up to 300mph!300mph!

On May 3, 1999 a total of 66 On May 3, 1999 a total of 66 tornadoes touched down across tornadoes touched down across

the state of Oklahomathe state of Oklahoma

It was the most prolific tornado It was the most prolific tornado outbreak in Oklahoma historyoutbreak in Oklahoma history

48 people perished during the 48 people perished during the outbreak outbreak

Hardest hit was Bridge Creek, Hardest hit was Bridge Creek, Oklahoma….Oklahoma….

…….where an F5 Tornado first touched down…..where an F5 Tornado first touched down….

before moving on tobefore moving on to…..

……Moore, Oklahoma where winds of Moore, Oklahoma where winds of 301mph were recorded301mph were recorded

36 of the 48 people who died during 36 of the 48 people who died during the outbreak that day, perished in this the outbreak that day, perished in this

tornadotornado

Total destruction caused by an F5 tornadoTotal destruction caused by an F5 tornado,, which which struck Moore, struck Moore, Oklahoma on May 3, 1999.Oklahoma on May 3, 1999.

Moore, OK Twister

Fig. 10-32, p. 288

Tornadoes occur most often in the central, Tornadoes occur most often in the central, Southeastern, and Midwestern parts of the U.S.Southeastern, and Midwestern parts of the U.S.

Fig. 10-28, p. 285

Tornado Tornado IIncidence by ncidence by SStatetate

NNumber of tornadoes reported by each state during a umber of tornadoes reported by each state during a 25-year period25-year period, and , and the average annual number of tornadoes the average annual number of tornadoes

per 10,000 square miles. per 10,000 square miles.

Fig. 10-31, p. 287

Tornadoes are composed of multiple vorticesTornadoes are composed of multiple vortices

Below is aBelow is a powerful multi-vortex tornado with powerful multi-vortex tornado with 33 suction vortices. suction vortices.

Fig. 10-29, p. 285

Average number of tornadoes during each month in the United StatesAverage number of tornadoes during each month in the United States

Table 10-1, p. 287

FeaturesFeatures associated with a tornado-breeding associated with a tornado-breeding supercell thunderstormsupercell thunderstorm

Fig. 10-38, p. 291

Fig. 10-36, p. 290

A tornado-spawning supercell thunderstormA tornado-spawning supercell thunderstorm. A. A hook echo in its rainfall pattern on a Doppler radar hook echo in its rainfall pattern on a Doppler radar

screen. The colors red and orange represent the screen. The colors red and orange represent the heaviest precipitation.heaviest precipitation.

Graduate students from Graduate students from the University of the University of Oklahoma use a Oklahoma use a

portable Doppler radar portable Doppler radar to probe a tornado near to probe a tornado near

Hodges, Oklahoma.Hodges, Oklahoma.

Fig. 10-39, p. 292

Video

Figure 3, p. 295