In October's issue of MMYC's Newsletter we went over what creates the wind that we need to propel our model yachts around the pond. In this issue I will explain weather information that affects surface wind in a local area. Doing so well help us understand what causes the local wind conditions and provide the added knowledge to improve our sailing.

The greatest factor that causes wind is High and Low Pressure Systems as they pass through an area. Wind is created with these two systems is because air flows from a high pressure system to a low pressure system. But there is more to it than that. By knowing what affects a pressure system can give the model yachter an inside track on what the wind will be like for a regatta.

For most of the Northern Hemisphere the wind moves from the west to the east (in the Southern Hemisphere it moves from the east to the west). Because of this we can generally expect a constant wind direction from west to east during clear, normal weather. As high and low pressure systems move from west to east, they are often associated with warm and cold air fronts. When this occurs, wind strength and direction is affected.

In the Northern Hemisphere, low pressure system winds flow in a counterclockwise direction into the low (clockwise in the Southern Hemisphere). A high pressure system's wind flows in a clockwise direction out of the high, (see Example 1). What this means is a high or low pressure system can change the direction of the surface wind from west to east. This change in wind direction with the location of the pond can affect the wind conditions at the pond thus causing a change in the sailing tactics.

For most of the time when a high or low pressure system moves through an area, it brings stormy weather, like high winds, rain, and hail. But this is not always the case, some high or low pressure systems don't have much strength and all that is produced is a slight increase in wind speed and clouds. The point here is pressure systems of low strength do have a positive effect by slightly increasing wind speed at the pond.

Another positive effect pressure systems is when a pressure system approaches the atmosphere pressure will start to change causing a change in the wind pattern. As a pressure system approaches, isobars are pushed closer together producing a rapid change in air pressure over a short distance, (see Example 2). When this occurs wind is generated, this is called pressure gradient force. The results at the pond are stronger, more stable winds which causes skippers to install the B sail rig.

An opposite positive effect occurs when a pressure system is moving away from an area. Usually a front has passed with the pressure system and the atmosphere pressure will start to spread out over a wider area. This is called gentle pressure gradient, and what this means for the model yachter is the wind slows down and start to flow back to its normal direction.

If the model yachter understands how winds forms and the affects of the weather on the wind, the model yachter can have a greater advantage in what to expect during a regatta. By this time you may think you know it all when it comes to wind, not quite. There is one more area that influences the wind, the surface of the earth. This is the one area of wind study that really makes a difference. To know it can put an edge on the knowledge and added performance on the water! Until next time, fair winds.