Ch 20Severe Weather

Storms and severe weather begin with WARM air rising. This LOW pressure and is considered UNSTABLE .

Cumulonimbus storm clouds

Thunderstorms-

• The circulation around any low pressure center, called a CYCLONE• Warm, unstable air, Low

Pressure• Cold Front, a cP air mass collides

with mT• Cumulonimbus clouds form.

• At any given time there are an estimated 2000 thunderstorms in progress on Earth

• Most frequent in Florida and the eastern Gulf Coast. (approx. 100 days/year

• East side of the Rocky Mt.s , with up to 70 days/year

• Why doesn’t the far west and northern third of states and Canada experience as many?

Hint: Think type of air mass

Tornados Violent windstorm that take the form of a rotating column of air, or vortex, extending down from a cumulonimbus cloud

(Conditions are present for formation) (funnel cloud has been sighted)

Measuring the intensity of tornados

Fujita Intensity Scale

Hurricanes Whirling tropical cyclones. Among the most violent and most destructive storms on Earth.

• Form in late summer over warm ocean waters where water evaporates creating huge amounts of water vapor in the air.• As the warm air rises latent heat is

released by condensation and the coriolois effect creates the cyclone

Eye – the high pressure center of the storm. Can be as large as 12 miles. No wind, calm.

Eye wall – the doughnut shaped area of intense cumulonimbus clouds and very strong winds that surrounds the eye. This is were the greatest wind speeds and heaviest rainfall occur. Storm surge occurs when the eye wall meets land.

Hurricanes diminish in intensity when:

• Move over ocean water that cannot supply warm moist tropical air

• Move onto land

• Reach a location where the airflow aloft is slowed

Measuring Hurricane Intensity