and stormy. The average temperature of the warmest month is higher than 10°C (50°F)
and the coldest month is below -3°C (-27°F). Snowfall is common and the cold temperatures
mean that snow stays on the ground for long periods of time. Trees grow in continental
climates, even though winters are extremely cold, because the average annual temperature
is fairly mild. Continental climates are not found in the Southern Hemisphere due to the
absence of a continent large enough to generate this effect.
Humid Continental (Dfa, Dfb)
Humid continental climates are found around the polar front at about 60oN latitude within
continental North America and Europe (Figure17.20). In the winter, middle-latitude cy-
clones bring chilly temperatures and snow. In the summer, westerly winds bring continental
weather and warm temperatures. The average July temperature is often above 20°C (70°F).
The region is typified by deciduous trees, which protect themselves in winter by losing their
leaves.
Figure 17.20: The humid continental climate zone covers much of the northeastern United
States, southeastern Canada and middle Europe. ( 18 )
The two variations of this climate are based on summer temperatures. In the humid con-
tinental climate withlong, hot summers(Dfa), the long summers and high humidity foster
plant growth (Figure17.21). Summer days may be over 38°C (100°F), nights are warm
and the temperature range is large, perhaps as great as 31°C (56°F)! In the humid conti-
nental climate withlong, cool summers(Dfb), summertime temperatures and humidity are
lower. Winter temperatures are below -18°C (0°F) for long periods. For example, Winnipeg,
Canada has a 38°C (68°F) annual temperature range.
Subpolar (Dfc)
Thesubpolarclimate is found between the humid continental and the polar tundra climates
(Figure17.22). This climate is dominated by long, very cold winters with very little pre-
cipitation. Continental polar air masses form when air stagnates in this zone. Snowfall is