The wind is often overlooked in weather, besides in thunderstorms and hurricanes when it is one of the key forms of damage. Wind can be a result of 2 weather phenomena, tight pressure gradients, or significant temperature gradients. On a tranquil day in the summer, wind can be caused by heating up the ground and making a temperature difference between the surface and air above our heads. The atmosphere has a "mixing layer" which is the layer of air that can mix with the ground. Typically it can mix about 1 mile into the air, but sometimes as much as 2 - 3 miles! Depending on the amount of sunshine and how unstable the atmosphere is, will help determine how windy it can be. If the atmosphere is mixing up to 5000 feet and the wind speeds at that level are 50 knots (~ 57.5 mph), these winds can be brought down to the surface using thermals. Thermals occur when the surface of the earth is heated and wants to rise, they rise up to the mixing level, mix with the temperatures aloft and sink back down to the surface. This process can continue as long as the surface continues to be heated by the sun. There can also be days when winds are weak in the mixing layer, so it will not be gusty at the ground.
Temperature gradients also can cause sea and lake breezes. Here's how it works: air over a body of water is typically colder than the land during the summer. This air sinks and becomes more dense. As the sun heats up the land, relatively warmer air forms and rises. This allows the cooler marine air to move inland and replace the warmer air, which rose and vacated the land mass. As this occurs, the cold air moving in from the lake or ocean acts like a mesoscale (small scale) cold front and can bring windier conditions as well. Interestingly enough, the sea breezes can also result in showers and thunderstorms, which are usually short lived but have the potential to become severe under the right conditions.
Courtesy NOAA / NWS
The 2nd way it can turn windy is with a pressure gradient. When there is a high pressure system relatively close to a low pressure system, the differences in pressure clash and the atmosphere tries to counteract it. The atmosphere likes to be in balance, so air from higher pressure flows towards lower pressure to try and stabilize itself.
