The general temperature pattern of middle latitude climates is well illustrated by daily temperature graphs of three stations at about the same latitude across North America. Victoria, British Columbia, on the west coast, occupies a windward position with respect to maritime polar air masses from the Pacific. Consequently, the contrasts between July and February (the two extreme months of the year) are small. Moreover, the daily ranges are small, especially in winter. The graph of Winnipeg, Manitoba, shows maximum continental influence with strong annual and daily contrasts. Note especially the wide fluctuations in winter, with outbursts of polar and arctic air bringing very low temperatures. St. Johns, New foundland, occupies a leeward position with respect to the continent and is accessible to maritime air masses from the Atlantic. It therefore has only a moderate annual temperature range, but the continental influence is nevertheless clearly marked in the sharply fluctuating daily temperature record
Three major types of natural vegetation and their associated soils may be recognized in the humid continental climate. The distribution is well illustrated in North America.
In the more humid eastern sections, including the warmer parts of the humid continental climate zone (Dfa), natural vegetation is summer green deciduous forest. Here soils are of the brown forest and gray-brown podzolic types, rich in humus and moderately leached so as to have a distinct light-colored leached zone under the upper dark layer. In this region, diversified farming and dairying are the most successful uses of the land where topography is favorable.
A northern belt of needleleaf evergreen forest extends along the entire length of the colder northern parts of the humid continental climate zone (Dfb). To this may be added the mountain regions of the Adirondacks and northern New England. Here soils are of the podzol type, strongly leached, but with an upper layer of humus. Cool temperatures inhibit bacterial activity, which would destroy this organic matter in tropical regions. Podzols are deficient in calcium, potassium, and magnesium, and are, in general, acid in chemical nature. Thus they are not highly productive for crop farming, even though adequate rainfall is generally assured. The podzols are, however, well suited to the growth of conifers.
The drier plains areas of the humid continental climate support a natural tall-grass prairie, which grades into the drier steppe regions of short grasses to the west. The prairie soils and chernozem soils, two major soil groups of these grasslands, are typically dark in colour and consist of a single, thick upper layer grading into the parent soil material below. These soils contain abundant calcium, magnesium, and potassium because rainfall is here distinctly less than farther eastward and leaching is less active as a soil-forming process.
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