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The Maine Geological Survey began a continuing process of mapping sand and gravel aquifers beginning in 1978. Statewide, Maine receives an annual rainfall total of 42 inches or 24 trillion gallons. Up to 50% of rainfall runs off the landscape in rivers and streams, while an additional 30–40% evaporates or is transpired through vegetation.
Mountain and valley breezes are other examples of local winds caused by an area's geography. Campers in mountainous areas may feel a warm afternoon quickly change into a cold night soon after the sun sets. During the day, the sun warms the air along the mountain slopes. This warm air rises up the mountain slopes, creating a valley breeze.
The warm air overrides the cooler air and moves upward. Warm fronts are followed by extended periods of light rain and drizzle due to the fact that, after the warm air rises above the cooler air (which remains on the ground), it gradually cools due to the air's expansion while being lifted, which forms clouds and leads to precipitation.
As warm, moist air rises up the windward side of a mountain, the air temperature cools and loses its capacity to hold moisture. Thus, the greatest amount of rainfall is expected at mid-altitudes and can support deciduous forest development. Above a certain elevation the rising air becomes too dry and cold, and thus discourages tree growth. [9]
"The mountains act as a blocking mechanism causing the cold air to get trapped, only being able to move southward on the eastern side of the mountains." Cold air damming events can last for ...
Much of the Great Lakes has little ice cover, leaving the exposed water to warm the Arctic air somewhat. However, persistent cold air will cause the ice cover to increase substantially. As the ice ...
Thus, hot air tends to rise and transfer heat upward. This is the process of convection. Convection comes to equilibrium when a parcel of air at a given altitude has the same density as its surroundings. Air is a poor conductor of heat, so a parcel of air will rise and fall without exchanging heat.
Warm air has a lower density than cool air, so warm air rises within cooler air, [8] [better source needed] similar to hot air balloons. [citation needed] Clouds form as relatively warmer air carrying moisture rises within cooler air. As the moist air rises, it cools causing some of the water vapor in the rising packet of air to condense. [9]