What causes San Francisco's famous fog?
The California Current travels from the north and brings cold water to the region just offshore. The warm Mediterranean climate of coastal California contrasts with the cold water offshore and forms advection fog, which blows off the shore and up to a few miles inland. Fog under the Golden Gate Bridge is a common sight in the City by the Bay.
When a particular location is near an ocean or large lake, the body of water plays an extremely important role in affecting the region’s climate.
- A maritime climate is strongly influenced by the nearby sea. Temperatures vary a relatively small amount seasonally and daily. For a location to have a true maritime climate, the winds must most frequently come off the sea.
- A continental climate is more extreme, with greater temperature differences between day and night and between summer and winter.
The ocean’s influence in moderating climate can be seen in the following temperature comparisons. Each of these cities is located at 37oN latitude, within the westerly winds (Figure below).
How does the ocean influence the climate of these three cities?
The climate of San Francisco is influenced by the cool California current and offshore upwelling. Wichita has a more extreme continental climate. Virginia Beach, though, is near the Atlantic Ocean. Why is the climate there less influenced by the ocean than is the climate in San Francisco? Hint: Think about the direction the winds are going at that latitude. The weather in San Francisco comes from over the Pacific Ocean while much of the weather in Virginia comes from the continent.
The temperature of the water offshore influences the temperature of a coastal location, particularly if the winds come off the sea. The cool waters of the California Current bring cooler temperatures to the California coastal region. Coastal upwelling also brings cold, deep water up to the ocean surface off of California, which contributes to the cool coastal temperatures. Further north, in southern Alaska, the upwelling actually raises the temperature of the surrounding land because the ocean water is much warmer than the land. The important effect of the Gulf Stream on the climate of northern Europe is described in "Concept Water on Earth."
- A maritime climate is influenced by a nearby ocean. A continental climate is influenced by nearby land.
- The temperature of offshore currents affect nearby land areas.
- A maritime climate is less extreme than a continental climate because the ocean moderates temperatures.
Use this resource to answer the questions that follow.
1. What does the temperature depend on?
2. What influences the weather in California?
3. What is the temperature variation between the coast and inland in the summer?
4. What is the temperature variation between the coast and inland in the winter?
5. How much rainfall does the redwood forest receive?
1. If upwelling stopped off of California, how would climate be affected?
2. From which direction would weather come to a city at 65-degrees north?
3. Why is the climate of San Francisco so different from the climate of Virginia Beach when both are near an ocean?