Canada’s Physical Geography Climate and Weather Part II Unit 2 Chapter 2

Regional Factors: Air temperature drops as altitude increases and air pressure decreases. The air pressure decreases as the air expands and its molecules move farther apart, which results in lower oxygen levels and cooling. The rate of change of temperature with elevation is called the environmental lapse rate. It explains why mountain climbers at high altitudes often require supplementary oxygen. This effect is seen in summer storm clouds called a cumulonimbus. Altitude

Bodies of Water In summer water heats up more slowly than land but in the winter it retains its heat for a longer period of time. As a result, bodies of water such as lakes and oceans influence climate. The Great Lakes affect the climates of neighbouring areas. In winter, the water warms the air and moisture falls as rain or snow. In summer, onshore winds may cool the land. In fall, the slow release of heat from the lakes may delay the first frost.

Mountain Barriers The Coast Mountains of BC experience some of the most precipitation (rain and snow) in Canada. These mountains are In the path of prevailing warm, wet, westerly winds, called the Westerlies. These same mountains keep the interior Fraser Plateau comparatively dry. The Rocky Mountains also cause air from the west to rise and cool. Resulting in the west-facing windward sides being wetter than the east facing leeward sides. These sides are said to be in a rain shadow. (Figure 2.20)