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<br />conditions where air warms at the surface or cools aloft and where <br />conditionally unstable air is lifted by orographic barriers. by cold <br />fronts. by convergence in low-pressure areas and by vertical divergence <br />where wind speeds are reduced as air enters land areas from the ocean. <br /> <br />Section 2.04 Topographic effects <br /> <br />Any oroqraphic barrier that causes air to be lifted or deflected <br />upward tends to initiate convective action and consequent precipitation. <br />Thus island and mountain peaks often are surrounded by clouds and rain. <br />As the air masses pass such a barrier, moisture precipitates on the <br />windward side of the barrier and as it subsides and warms on the leeward <br />slope the remaining air mass becomes dry. Consequently, where wind <br />patterns are steady, the windward side of mountains received precipitation, <br />and the leeward side is desert. <br />Since most of the air's moisture is in the lowest 2.000 meters, <br />heaviest precipitation usually occurs below 3,000 meters elevation. <br />Moisture condensed at lower elevations can be carried to elevations <br />of 3.000 meters by high winds. Because of irregularities in mountain <br />surfaces. local wind patterns develop that can depend on wind direction <br />or that can be rather uniform from time to time. In either event. there <br />is a tendency for large variations in precipitation from place to place <br />within mountainous regions. This pattern cannot easily be related to <br />topographic features because of the extreme complexity of wind and <br />moisture condensation interactions. Nevertheless, there is a general <br />pattern of higher precipitation with higher ground elevations and with <br />the degree of windward exposure of the ground surface. <br /> <br />Section 2.05. Storm transposition <br /> <br />The fact that meteorological conditions vary only gradually within <br /> <br />2-05 <br />