Overview
 All t’storms are not created equal
 Severe thunderstorms produce the most violent
weather conditions on Earth
 Supercells – characterized by intense, rotating
updrafts; can last several hours and have updrafts up to
240 km/h.
 In the U.S., less than 10% of storms are severe
Lightning
 Lightning is electricity caused by the rapid rush of air
in a cumulonimbus cloud
 Lightning forms when and advancing stepped leader
unites with an upward moving return stroke
 A bolt heats the air around it to 30,000 degrees Celsius,
producing thunder
 7500 forest fires, 300 injuries, 93 human deaths each
year
Damaging Wind
 Downbursts are violent downdrafts concentrated in a
certain area; could be more than 160 km/h
Hail
 Causes $1 billion in damage in the U.S. each year
 Largest recorded hailstone weighed 1.67 punds
 First, water droplets collide with ice pellets and they
freeze instantly forming larger pellets
 Updrafts and downdrafts cause more collisions
Floods
 The leading cause of weather related deaths
 More rain falls in an area than the ground can absorb
 More rain falls in an area than rivers and streams can
transport away from that area
Tornadoes
 A tornado is a whirling, violent column of air in contact
with the ground
 Tornadoes are associated with supercell thunderstorms and
begin as a funnel cloud
 Wind shear allows the formation of a tornado
 Classified using the Fujita intensity scale (F0 – F5)
 Most form in spring during the late afternoon
 80 deaths and 1500 injuries occur in the U.S. each year