Geography Reference
In-Depth Information
In continental regions, winters are harsh, but summers are hot, even sweltering,
in many parts of the southern half of the country (see Figure 1.7). The Southwest
states hold the records for hot temperatures.
Average temperatures exceed 90°F (32.2°C) 169 days per year in Phoenix,
Arizona, 133 days in Las Vegas, Nevada, and 109 days in El Paso, Texas, in
normal
5
years.
While the coastal climate of California is moderated by a cold current, the
number of annual days of excessive heat goes from one in San Francisco to 108 in
Fresno in the Central Valley. High altitudes limit the duration of any excessive heat
to less than two months in the mountains of the West and in the high plains, but the
Great Plains south of the 35th parallel suffer from torrid heat. In Dallas, for
example, a heat wave lasts an average of 97 days.
The Southeast is also very hot, with the number of days of excessive heat
climbing up to 105 days in Orlando, Florida.
The Great Lakes help cool the Northeast. Chicago has an average of only 17
days of excessive heat per year. The influence of the ocean climate also keeps the
Pacific Northwest cool.
For a long time, summer heat and humidity discouraged settlement in the South,
with the exception of the coast of California. According to Meinig [MEI 04], the
change occurred in 1951 when cheap, domestic air-conditioners were first sold. The
harshness of climates in the US contributes to explaining the very high energy
consumption in the United States, whether for heating in winter or air-conditioning
in summer.
The emission of more than 25% of the global production of greenhouse gases by
a mere 5% of the world's population is indeed also the unfortunate result of the high
level of comfort in which Americans live, despite their harsh climate.
Among the violent weather phenomena that particularly affect the United States,
a special mention should be made with regard to tornadoes and hurricanes.
Tornadoes are especially common in spring in the Great Plains, where polar and
tropical air masses clash abruptly (see Figure 1.8).
5
. Seasonal “normal” climate data from the NOAA is based on averages calculated from
observations made between 1970 and 2000.
