Objective: SWBAT explain how various storms form

WARM UP:1. Using page 46 of the little

blue book, DRAW the symbol for each weather front

Storms: Tornadoes

What did you draw?

Station Model Practice

What DIRECTION is the wind blowing?What WIND SPEED is shown? (use your key from hw sheet)What is the CLOUD COVER?

Wild Weather: Storms!

• Storm: violent disturbance in the atmosphere• Sudden changes in air pressure• Rapid air movements

Storms

• Hurricanes• Tornadoes• Blizzards• Thunderstorms• Lake-effect snowstorms (mostly in the Great

Lakes Region)• Ice storms

Tornadoes

Tornado A violently rotating column of air

(vortex), hanging from a cumulonimbus cloud, with circulation that touches the surface of the earth

Tornado Damage

Tornadoes mainly cause damage by picking up something and throwing it through the air or hurling objects against something

A 20-ton trailer blown off U.S. 30; it bounced 5 times

A pick-up truck caught in the path of a tornado

The Supercell

Tornado forms here

Tornadoes form from thunderstorms which contain one or more updrafts (upward moving air which is warm and moist).

These updrafts form towering cumulonimbus clouds which race upward and cool to form ice crystals (once they reach the anvil of the thunderstorm).

Severe thunderstorms, which is an intense thunderstorm with winds of at least 60 mph, most likely produce tornadoes.

Tornado 101

Tornado Formation

Beginning Stage: Tornado begins as a rotating wall cloud which quickly evolves into a funnel

Early Stage: Tornado funnel develops

(may be transparent) and extends down from the cloud to the ground

Mature Stage: Tornado funnel reaches maximum width as well as maximum intensity then begins to shrink

Decay Stage:

tornado may remain stationary and take on a ropelike appearance before dissipating

Tornado Categories

• The Fujita-Pearson Tornado Intensity Scale or F-scale ranks tornadoes by their wind speed.

• signs of f5

• F0- winds 40-72 mph• F1- winds 73-112 mph• F2- winds 113-157 mph• F3 – winds 158-206

mph• F4 – winds 207-260

mph• F5 – winds > 261 mph

Tornado Facts1. Tornadoes are 400-500 feet wide. Tornadoes

have winds around 100 miles per hour.2. Tornadoes last only a few minutes.3. Some monster tornadoes are a mile wide, have

winds up to 300 mph, last an hour or more, and travel 200 miles.

4. Tornadoes occur most often in the spring (April- June)

5. Most tornadoes in the US occur along “Tornado Alley,” an area that runs from Texas to Illinois.

Where Tornadoes Occur

Tornado Alley covers the Great Plains states

When Tornadoes Occur

• Anytime of the year- usually in the spring, summer, and fall

• Most tornadoes occur during late spring in the month of May

• Between the late afternoon and early evening is when most tornadoes are spawned

• The most dangerous time for formation during evening hours

A typical late afternoon tornado

Tornado Occurrence by Category

F0 Category

• (Weak) winds (40-72) mph , little damage• Damage: tree branches snapped, chimneys toppled,

signs torn down

F3 Category

• (Strong) winds: (158-206) mph, severe damage• Damage: most trees uprooted, trains overturned,

roofs torn off, walls demolished

F5 Category

• (Violent) winds: (261- 319) mph, incredible damage; rareDamage: bark peeled off trees, houses lifted off foundations,

vehicles travel greater than 100 m through the air

Satellite image taken May 3, 1999 @ 645 CDT

Other types…Microburst

Microbursts are downdrafts from thunderstorms consisting of a narrow column of cool air traveling at high speeds which can cause damage similar to a weak tornado over a small area

Other types…Waterspouts

A waterspout is a tornado that forms over a body of water, or a tornado that moves from land onto water

Signs of a Tornado!• A greenish colored sky associated with the

thunderstorm (caused possibly by the scattering of light by particles in the sky)

• A sudden drop in barometric pressure• Large hail of at least .75 in. diameter• Strong winds > 60 mph• Frequent and intense lightning• A rotating wall cloud or a cloud that

appears to hang from the sky• A loud rumbling noise- seek shelter!

Mammatus clouds Green sky

Early Warning Systems

The National Storm Prediction Center constantly monitors the weather and radars across the U.S. They are responsible for issuing tornado watches and warnings.

• Tornado Watch: a parallelogram is drawn around a 10,000 mi.^2 s area where the atmosphere seems to possess the conditions necessary for tornado development (severe thunderstorm)

• Tornado warning: a county has a thunderstorm which appears to have produced a tornado or someone has physically spotted a tornado, apparent funnel, or observed damage from what could be a tornado! SEEK SHELTER IMMEDIATELY!!

Tornado Precautions

• Go to a basement, if you have one.• Get in the innermost room of your

house. Avoid rooms with windows. Bathrooms are good.

• Crouch with arms above your head.

• If outside, lie in a ditch or get under a bridge.

• If you live in an area with a frequency of tornadoes, listen to forecasts.

• Witness- Joplin Tornado (start at 23:44)

TornadoesWrite Time!Why would tornadoes most likely occur late afternoon in

warm to moderate temperatures? Explain using the words Heat, Low Pressure, Density,

and Rises