In the last unit we looked at how wind patterns develope on a global basis. This unit discusses wind patterns on a local or more regional level.
First off, lets look at how winds are produced.
The above diagrams show in the broadest sence how winds are produced. Air flows from an area of high pressure to an area of low pressure. The next question shoul be "What cases areas of high and low pressure?"
One such cause is heat gradients resulting in convection currents. If air is heated it becomes less dense and will rise. On cooling air becomes more dense and will drop. (Same idea as in a Hadley cell).
During the day the a land mass will absorb solar energy and becomes warm. This will cause the air above it to also become warm and as such will rise. As the warm air rises, cooler air will move in to replace this warm air. Do remember the two convection current experiments that were done in class.
The local convection current set up during the day is called a thermal.
Thermals that form near bodies of water, a lake or a sea, produce what is called a sea breeze
In the evening when the water becomes warmer than the land (remember the experiment on heat capacity were it was shown that water will hold a lot of heat), you get what is called a land breeze in which the wind flows off the land and out over the body of water.
Lake-Effect Snow will occur on the downwind or leeward side of a large lake where the prevailing winds tend to produce local precipitation. For example, just this winter over Christmas, Hamilton received almos no snow. However, Buffalo, only 100 km east, recived almost 2.5 meters of snow in a three day period. Buffalo's geographical locations meets all the requirements for lake- effectsnow.