Seasonal changes in the earth's position relative to the sun causes the shift from winter to spring. Spring wind, the characteristic weather condition, is responsible for the weather, the food chain and, to some degree, the landscape. The source for the seasonal change begins as the earth, tilted on its axis toward the sun, heats the earth's surface in our region. A high-pressure air mass, the North Pacific High, forms as warm air rises offshore. As it strengthens, it buffers the Bay Area from storm systems.
Clear skies prevail, allowing the sun's warm rays to dry the soggy landscape.
The Central Valley heats up. The resulting rising air mass is substantial enough to create an area of low-pressure, the Central Valley Low. On its way it sweeps over us. Gusts are especially strong on clear, sunny days. A walk across the Golden Gate Bridge against these winds is testimony to the force of this gradient.