Thunderstorms

2009

Storms • A violent

disturbance in the atmosphere.

• Involve sudden changes in air pressure, which cause rapid air movement.

Thunderstorms • Heavy rainfall with

thunder and lightning.

• Form within cumulonimbus clouds.

• Warm air rapidly rises, causing updrafts that bring moisture to the tops of the cloud.

• The moisture condenses, and eventually forms rain.

TS Ingredients

• Thunderstorms need three things:

• Moisture - to form clouds and rain.

• Unstable Air - relatively warm air that can rise rapidly.

• Lift - fronts, sea breezes and mountains are capable of lifting air to help form thunderstorms.

When Do Ts Occur?

• Most likely to occur in the spring and summer months and during the afternoon and evening hours.

• Can occur year-round and at all hours of the day or night.

• Along the Gulf Coast and across the southeastern and western states, most thunderstorms occur during the afternoon.

• Thunderstorms often occur in the late afternoon and at night in the Plains states.

Facts

• Thunderstorms affect small areas when compared with hurricanes and winter storms.

• The typical thunderstorm is 15 miles in diameter and lasts an average of 30 minutes.

• Nearly 1,800 thunderstorms are happening at any moment around the world.

Life Cycle of thunderstorms

• All thunderstorms, whether or not they become severe, progress through a life cycle which may be divided into three main stages

Developing Stage

• Moist air, heated by the sun, rises which causes an updraft of air.

• As warm air rises, it cools and forms clouds. As the water vapor condenses it gives its energy to the surrounding air, making it warmer and causes it to rise more. This energy powers the thunderstorm.

• Usually little if any rain during this stage.

• Lasts about 10 minutes • Occasional lightning

Mature Stage

• Most likely time for hail, heavy rain, frequent lightning, strong winds, and tornadoes.

• Storm occasionally has a black or dark green appearance

• Lasts an average of 10 to 20 minutes but may last much longer in some storms.

Dissipating Stage

• Rainfall decreases in intensity

• Can still produce a burst of strong winds

• Lightning remains a danger • When the downdrafts in the

cloud begin to dominate over the updrafts, this happens

• Since warm moist air can no longer rise, cloud droplets can no longer form

• The storm dies out with light rain as the cloud disappears from bottom to top

Thunderstorm Stages

Single-cell Thunderstorm

• A single, isolated

thunderstorm

• Have a lifespan of

about 30 minutes

• Are not very severe

• Very rare and occur

randomly

• Are difficult to

forecast

Multi-cell Cluster Storms

• Are the most common

type of thunderstorms

• Occur in a group

• Persist for a few hours

• Produce modern size

hail

• Weak tornadoes occur

during this storm

Multi-cell Line storm

• Consists of long line thunderstorms usually associated with fronts.

• Can produce hail the size of golf balls

• Weak tornadoes

• Can easily be predicted with the help of radar

Super Cell

• Although rare, highly organized thunderstorms

• Pose of high threat to life and property, as

these can produce strong to violent tornadoes

Thunder and Lightning • Friction between

updrafts and downdrafts cause electrons to be stripped from some atoms and given to others. Just like walking across a carpet in your socks.

• So the clouds develop charges.

• Lightning is the spark when the discharge occurs.

• Lightning is one big static electricity discharge!

What Causes Lightning?

• In a cloud, swift air

separates water droplets,

causing electrical

charges.

• The electrical charges

build up and causes huge

electric shocks. It

generates about 100

million volts of electricity.

Thunder

• Thunder is caused by lightning.

• When a lightning bolt travels

from the cloud to the ground it

actually opens up a little hole in

the air, called a channel.

• Once then light is gone the air

collapses back in and creates a

sound wave that we hear as

thunder.

• The reason we see lightning

before we hear thunder is

because light travels faster than

sound!

How Far Away?

• Sound travels roughly 1-km in 3 seconds or 1-mile in 5 seconds.

• So if you see the flash of lightning, and it takes 10 seconds for the thunder to reach you, the lightning was about 2 miles away.

Forked Lightning

• Forked lightning: Bolts that most commonly occur between clouds and the earth.

Ball Lightning

• Ball lightning:

• A very rare.

• It is a sphere shape

that glows and

moves slowly.

• It forms in a storm

cloud, and can last

five seconds.

Heat Lightning

• Heat - Lightning from

storms that are so far

away that we can't

hear the thunder or

see any rain.

Sheet Lightning

• Sheet Lightning: covers a wide area, and can be inside or

between clouds.

Thunderstorm Safety • Go inside! • Get in car if you can’t make it to

a sturdy building (basements are good).

• If caught outside, stay away from tall objects like trees.

• Make sure that you are not the tallest object by crouching down. Crouch down, bend forward, and grab your ankles. Keep your head down. Do not lie flat on the ground and try to keep out of puddles or other standing water.

• Do not use a phone or a computer during a thunderstorm.

• Do not take a shower or wash dishes.

• If there are downed power lines anywhere around you, DO NOT touch them

Thunderstorm Watch/Warning

• Severe Thunderstorm

Watch -conditions are

conducive to the

development of severe

thunderstorms in and

close to the watch area.

• Severe Thunderstorm

Warning - a severe

thunderstorm has

actually been observed

by spotters or indicated

on radar, and is

occurring or imminent in

the warning area. Time

to take cover!