Strong winds are most often caused by air moving from an area of high atmospheric pressure to an area of low pressure quickly over a small distance. This is called a strong pressure gradient force.
Even light winds are normally caused by air moving between areas of different pressures. A pressure gradient represents how quickly the atmospheric pressure changes over a space. When the pressure changes quickly in a short distance, the pressure gradient force in the area is large and creates strong winds.
What the wind blows over can also have an impact on its speed. Open areas, such as lakes, experience faster winds than a forest does. The trees in the forest help slow the wind down by friction. When solid objects such as buildings are hit with wind, they can funnel the wind between them and cause the wind to gain speed.
Thunderstorms also have the ability to create strong winds. Rain from the storm evaporates below the cloud, causing the air to cool beneath it. This cold air is heavy and crashes into the ground below. When it hits the ground, this cold air must turn sideways, and the result is strong winds. These winds are known as microbursts. Wind speeds in microbursts can exceed 100 mph and cause significant damage even though they only last for five to 15 minutes.