Severe Storms Classified under severe storms are thunderstorms

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

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.

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. – F 0 F 5 (see page 574)

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)

Hurricanes (cont’d) • 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.

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