Climate Controls for San Francisco

Topography 
San Francisco's topography lies at the boundary between the Pacific Ocean on the West, San Francisco Bay to the East and the Golden Gate to the North. San Francisco’s highest peak is toward the South, measuring at over 900 feet in elevation (Mount Davidson's peak of 938 feet the tallest, followed closely by Mount Sutro at 920 feet and both North and South Twin at 919 feet). In addition to the steep topography, ridge lines and high hills are abundant in this region. The city's steepness is shown by the fact that the 60 meter elevation contour is generally within one mile of sea level.

Latitude
37.7833° N, 122.4167° W. San Francisco is located in the mid- latitude region and on the west coast of the North American continent, giving it a Mediterranean type climate (Koppen type Cs). The Bay area is categorized by having moist mild winters and dry summers.

Elevation
Sea level.

Nearby Water 
San Francisco's climate is influenced by its location in the northern end of a peninsula, surrounded on three sides by the relatively cool waters of the Pacific Ocean and San Francisco Bay. In addition to the normal cool temperatures of the mid-latitude Pacific Ocean, the water temperatures are modified by the up welling of cold water along the California coast.

Air Masses and Prevailing winds 
San Francisco is affected by maritime air masses. The persistence of the Pacific High and the Northwest winds are prevalent in this region. During the winter, these systems are driven southward; the Pacific High, the Westerlies and the jet stream dips south of 40 degrees N. Winter thunderstorms occur on the average only twice per season in cold unstable post-frontal air masses. While most storms during these periods produce light precipitation, the occasional coupling of polar and subtropical air masses can produce heavy rainfall events.

Miscellaneous
The San Francisco Bay Area is another city on the West Coast which is sporadically affected by a Pineapple Express. When the Pineapple Express is present, heavy, persistent rainfall naturally causes flooding in and around the city.

Figure 1.

In Figure 1, the trend line for July’s temperature maximum does appear to be declining. In 1964, the trend line begins at a 90 degree average and steadily drops to a 84 degree average in 2012. The trend line for January’s temperature maximums appears to be steady in the 50 year span.

                   

Figure 2. 

In Figure 2, the Trend line for July’s minimum temperatures are steadily rising; beginning at a 49 degree average in 1964 and ending at a 51 degree average in 2012. Conversely, January minimum temperatures are significantly increasing; beginning at a 32 degree average in 1964 and ending at a 38 degree average in 2012.  

In hindsight, San Francisco minimum temperatures are increasing considerably while the maximum temperatures are slightly decreasing, overall there appears to be a slight warming occurring in the Bay Area.

San Francisco vs. Long Beach

                               

Figure 3.

  

Location and Topograpy

Even though Long Beach and San Francisco reside in the same state, they both experience different micro-climates. Similarly, Long Beach and San Francisco are both categorized by having a Mediterranean climate; however, their precise location and unique topography results in slight climatic differences. Both cities sit along the coast line; however, Long beach is virtually flat whereas San Francisco has steep mountainous terrain and high hill topography. Topography can dictate the path of an air mass’s course.  Long Beach specifically lays directly east of the Palos Verdes Peninsula; paired with its mostly south facing coastline, the barrier blocks east to west airflow and a significant amount of the coastal moisture that affects areas such Manhattan Beach and Santa Monica. As mentioned above, San Francisco's topography lies at the boundary between the Pacific Ocean on the West, San Francisco Bay to the East and the Golden Gate to the North.

Fog

San Francisco fog rolls in off the ocean, quickly covering various areas of the city, and then disappearing just as quickly. The infamous San Francisco fog is usually seen on summer mornings, coming off the cooler ocean and backing up against the hills, but it also comes from the colder inland areas during the winter. Similar to the San Francisco fog, Long beach experiences low clouds and fog frequently (usually in the summer), developing overnight and blanketing the area on many mornings. This fog usually disappears by the afternoon, and a westerly sea breeze often develops, keeping temperatures moderate.

Air Mass and Precipitation

San Francisco has bodies of water just to the west where rain and wind come in with little resistance.  The North Bay typically receives the most rain, aided by orographic lifting from the nearby mountains and its northern location that lies in closer to the path of the polar jet stream during the winter months. Since most storms come from the northern Pacific and shed water as they move south, San Francisco is more likely to receive more rain than Long Beach. Conversely, Long Beach is somewhat protected by the San Jacinto and Santa Rosa mountain ranges, which act as a barrier to keep the warm and dry Continental Tropical (cT) air mass away from the coastal area. Despite, some of the contrasts in precipitation trends, both cities resemble similar temperature patterns.

 

Figure 4. 

Figure 5.

The average temperature in Long Beach, Ca, 64.4 degrees Fahrenheit.
The average annual precipitation is 14.45 inches.
The average temperature in San Francisco is 57.2 degrees Fahrenheit.
The average annual precipitation is 20 inches

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Sources Cited

(Figure 1 and Figure 2 are original graphs produced by Sanaz Jazi.)

Accuweather. Image. Accuweather, 2014.Web. 1 May 2014.

Climatemps. Image. Climatemps, 2013. Web. 5 May 2014.

Climate of San Francisco. Ggweather. Golden Gates Weather Service, 2014. Web. 5 May 2014.

National Weather Service Forecast Office. NOAA, 2014. Web. 5 May 2014.
Usaclimatetemps. Your weather service, 2014. Web. 5 May 2014.