Wind is simply the air in motion. Usually when we are talking about the wind, it is the horizontal motion we are concerned about. If you hear a forecast of west winds of 10 to 20 mph that means the horizontal winds will be 10 to 20 mph form the west. Although we cannot actually see the air moving, we can measure its motion by the force that it applies on objects. For example, on a windy day leaves rustling or trees swaying indicate that the wind is blowing. Officially, a wind vane measures the wind direction and an anemometer measures the wind speed. The vertical component of the wind is typically very small compared to the horizontal component, but is very important for determining the day-to-day weather. Rising air will cool, often to saturation, and can lead to clouds and precipitation. Sinking air warms causing evaporation of clouds and thus fair weather.
Surface maps are marked with H's and L's which indicate high and low pressure centers. Surrounding these "highs" and "lows" are lines called isobars. "Iso" means "equal" and a "bar" is a unit of pressure so an isobar means equal pressure. We connect these areas of equal pressure with a line. Everywhere along each line is constant pressure. The closer the isobars are packed together the stronger the pressure gradient is. Pressure gradient is the difference in pressure between high and low pressure areas. Wind speed is directly proportional to the pressure gradient. This means the strongest winds are in the areas where the pressure gradient is the greatest.
Three forces cause the wind to move as it does. All three forces work together at the same time. The pressure gradient force is a force that tries to equalize pressure differences. This force causes high pressure to push air toward low pressure. Thus air would flow from high to low pressure if the pressure gradient force were the only force acting on it. However, because of the earth's rotation, there is second force, the Coriolis force that affects the direction of wind flow. Named after Gustav-Gaspard Coriolis, the French scientist who described it mathematically in 1835, this force is what causes objects in the northern hemisphere to turn to the right and objects in the southern hemisphere to turn to the left.
Rain is liquid precipitation and is a product of the condensation of atmospheric water vapor that falls under gravity. In order for cloud droplets, which are very small, to become raindrops, they have to increase in size almost a million times. Coalescence generally happens most often in clouds above freezing, and is known as the warm rain process. In clouds below freezing, when ice crystals gain enough mass they begin to fall. This generally requires more mass than coalescence when occurring