Severe Storms

1
Severe Storms

• Classified under severe storms are thunderstorms,
  tornadoes, and hurricanes.

2
Thunderstorms

• Thunderstorm produces thunder and lightening
  and possibly heavy rain, gusty winds, and hail.
• Can be local, single cloud storms, or multiple
  cells along a cold front.
• Development of thunderstorms involve 3 stages.
• Cumulus Stage warm, moist air is moved upward.
• Mature Stage (about 1 hour later) heavy
  precipitation begins with gusty winds, lightning,
  and hail.
• Dissipating Stage cooling of the air ? the
  storm to dies down.

3
Tornadoes

• Tornadoes violent windstorms that form a
  rotating column of air (vortex) that extends
  downward from a cumulonimbus cloud.
• Most form during thunderstorms.
• Begins with a strong wind high up in the
  atmosphere that causes winds lower in the
  atmosphere to roll horizontally ?strong
  thunderstorm updrafts will cause the mesocyclone
  to tilt until it is standing upright.
• The intensity of a tornado is based on the wind
  speed and the estimated damage.
• F0 ? F5 (see page 574)

4
Hurricanes

• Hurricane whirling tropical cyclone that
  produces winds of at least 119 km (74 mph) in the
  U.S.
• Develop in late summer when the water
  temperatures are warm enough to provide enough
  heat and moisture to the air.
• Tropical Depression (disturbance) first stage
  with several thunderstorm clusters and little or
  no cloud rotation.
• Tropical Storm winds begin to rotate and
  thunderstorms progress.
• Hurricane rotating cloud with winds of 119
  km/hour or more.
• Intensity of a hurricane is based on the wind
  speeds.
• Category 1 is lowest with wind speeds of 119
  km/hr.
• Category 5 is the most intense with wind speeds
  above 249 km/hr. (see page 577)

5
Hurricanes (contd)

• Eye center of the hurricane where air is
  subsiding (sinking) and being warmed.
• Eye Wall the layer of clouds that surrounds the
  eye, where winds are fastest and rainfall is
  greatest.
• Rain Bands clouds that extend outward from the
  eye wall and circulates and rotates around the
  storm cell.
• Storm Surge a dome of water directly underneath
  the eye of the hurricane which can cause severe
  flooding as the storm hits landfall.

6
Assignment

• Warm and Cold Front Questions
• ? A satellite image of Hurricane Fran