can also be found north of where it is usual. Winds coming from a different direction can
also make a region hotter than normal. Temperatures that would not ordinarily be too hot
may create a heat wave if the humidity rises too high.
More people die from extreme heat on average each year than in any type of storm. The
Chicago Heat Wave of 1995 killed about 600 people who did not have access to air condi-
tioning. The world was shocked in July and August 2003, when between 20,000 and 35,000
died in a European heat wave, mostly in France (Figure16.37).
Figure 16.37: Temperature anomalies (outside of the normal, expected range) across Europe
in the summer of 2003. France was the hardest hit nation. ( 26 )
Droughtstrikes a region if it has less rainfall than normal for days, weeks, or years, de-
pending on its location. A normally wet city enters drought at a much greater rainfall level
than a city located in the desert. A location may also be experiencing drought, even if it
receives rain, if the rain falls so that it is useless to humans. For example, a heavy rain may
run off a dried out landscape rather than sinking into the soil and nourishing the plants.
Lesson Summary
- Thunderstorms arise in warm weather when updrafts form cumulonimbus clouds that
rain and hail. - Lightning and thunder result when positive and negative electrical charges in different
parts of the cloud and on the ground attempt to equalize. - Tornadoes form most commonly from thunderstorms. Although they are shorter in
duration and affect a smaller area than other severe storms, they do an enormous
amount of damage where they strike. - Cyclones of all sorts are large and damaging; they include nor’easters and hurricanes.
- Heat waves kill more people each year than any type of storm and mostly form in
regions beneath an unusually high pressure zone.
Review Questions
- Describe in detail how a thunderstorm forms and where the energy to fuel it comes
from. Start with a warm day and no clouds. - How does a thunderstorm break apart and disappear?
- When and why does a severe thunderstorm get more severe rather than losing energy
and disappearing? - How do lightning and thunder form?
- Discuss the pros and cons of living in an area that is prone to tornadoes versus one
that is prone to hurricanes.