Climate of the Los Angeles Basin

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The Santa Ana winds in Southern California sweep from the deserts and across the Los Angeles Basin pushing smoke from wildfires far out into the Pacific Ocean.

The Los Angeles Basin is noted for its moderate weather. The climate is classified as a Mediterranean climate, characterized by seasonal changes in rainfall—with a dry summer and a winter rainy season—but relatively modest transitions in temperature. Under the modified Köppen climate classification, the coast is classified as Csb and the inland areas as Csa.

Summers are warm, hot and dry, with an average August high/low at LAX of 76.6 °F (24.8 °C) and 64.2 °F (17.9 °C). The same figures at the University of Southern California downtown campus are 84.8 °F (29.3 °C) and 65.6 °F (18.7 °C). However temperatures sometimes exceed 90 °F (32 °C) during the summer. Winters are mild and somewhat rainy with high temperatures at LAX of 65.5 °F (18.6 °C) and lows of 47.8 °F (8.8 °C). Spring and autumn bring mild days with cool evenings and are generally dry.

The Los Angeles area is also subject to the phenomena typical of a microclimate. As such, the daytime temperatures can vary as much as 36 °F (20 °C) between inland areas such as the San Fernando Valley and San Gabriel Valley versus the coast in the Los Angeles Basin.

Most rainfall occurs during winter and early spring, typical of a Mediterranean climate. February is considered the wettest month. The first rainfall of the water year usually occurs in October or November, with rain becoming more common December through February. The rain events then begin to taper off in March, and April and May usually see only one or two rains. However, the timing and volume of rains in the winter is far from predictable. Most cold fronts and depressions spun off by the strong winter seasonal low-pressure area in the Gulf of Alaska fail to carry significant precipitable moisture as far south as Los Angeles. This is subject to the position and strength of the jet stream and strength of the Gulf of Alaska low, as well as continental airmasses. Some years, however, a well-developed series of cold fronts moves into the area with relatively short separation between each, bringing an intermittently rainy period to Los Angeles for several weeks.

Sometimes rainfall can occur in the summer from monsoon thunderstorms or even from remnants of dissipating eastern Pacific hurricanes, but this is unusual. Los Angeles averages 15.1 inches (384 mm) of precipitation per year, but is lower at the coast and higher at the mountains. Tornadoes are rare, however, weak-to-moderate-strength waterspouts sometimes occur during warm winter storms, although this is unusual. Snow is extremely rare in the Los Angeles basin, but the nearby San Gabriel Mountains typically receive snow every winter season. The greatest snowfall recorded in downtown Los Angeles was 2 inches (5 cm) on January 15, 1932.[1][2]

Overview[edit]

Santa Ana Winds[edit]

Main article: Santa Ana winds

The Santa Ana winds are strong, extremely dry offshore winds that characteristically sweeps across Southern California and northern Baja California during late fall into winter season. They range from hot to cold, depending on the prevailing temperatures in the source region, the Great Basin and upper Mojave Desert. Nevertheless, the winds are notorious for causing hot, dry weather due to compressional heating of the lower atmosphere.

Extreme Weather[edit]

In downtown Los Angeles, weather records began on July 1, 1877. The highest temperature recorded in downtown Los Angeles was 113 °F (45 °C) on September 27, 2010. The lowest temperature was 28 °F (−2 °C) on January 7, 1913 and on January 4, 1949.[12] The wettest year was 2005 with 37.25 inches and the driest year was 2007 with 3.21 inches. The greatest rainfall in one month was 14.94 inches (379 mm) in January 1969. The greatest rainfall in 24 hours was 5.68 inches (144 mm) on March 2, 1938.[13]

At the Los Angeles International Airport, the highest recorded temperature was 110 °F (43 °C) on September 26, 1963. The lowest temperature was 27 °F (−3 °C) on January 4, 1949. The wettest year was 1983 with 29.46 inches (748 mm) and the driest year was 1947 with 2.95 inches (74.9 mm). The greatest rainfall in one month was 13.79 inches (350 mm) in February 1998. The greatest rainfall in 24 hours was 5.60 inches (142.2 mm) on November 21, 1967.[14]

In Long Beach, the highest recorded temperature was 111 °F (44 °C) on October 16, 1958, and October 15, 1961, and again on September 27, 2010. The lowest temperature was 21 °F (−6 °C) on January 20, 1922. The wettest year was 1978 with 27.67 inches (703 mm). The driest year was 2002 with 2.63 inches (66.8 mm). The greatest rainfall in one month was 14.50 inches (368 mm) in January 1969, including a record 24-hour rainfall of 6.71 inches (170.4 mm) on January 20 that month. The record snowfall was 1.5 inches (3.8 cm) in January 1949.[15]

Sea temperatures[edit]

Average annual temperature of sea is 63 °F (17 °C), from 58 °F (14 °C) in January to 68 °F (20 °C) in August.[16]

Average sea temperature:[16]
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
58 °F (14 °C) 58 °F (14 °C) 60 °F (16 °C) 60 °F (16 °C) 61 °F (16 °C) 63 °F (17 °C) 66 °F (19 °C) 68 °F (20 °C) 67 °F (19 °C) 66 °F (19 °C) 64 °F (18 °C) 60 °F (16 °C) 63 °F (17 °C)

References[edit]

  1. ^ Rasmussen, Cecilia (2005-03-10). "We're Not in Kansas, but We Do Get Twisters - Los Angeles Times". Articles.latimes.com. Retrieved 2009-01-08. 
  2. ^ Burt, Christopher. Extreme Weather: A Guide and Record Book. New York: Norton, 2004: 100.
  3. ^ a b "NowData – NOAA Online Weather Data". National Oceanic and Atmospheric Administration. Retrieved June 7, 2013. 
  4. ^ "Station Name: CA LOS ANGELES DWTN USC CAMPUS". National Oceanic and Atmospheric Administration. Retrieved 2014-05-09. 
  5. ^ "LOS ANGELES/WBO CA Climate Normals". National Oceanic and Atmospheric Administration. Retrieved October 20, 2013. 
  6. ^ "Station Name: CA LOS ANGELES INTL AP". National Oceanic and Atmospheric Administration. Retrieved 2014-05-09. 
  7. ^ "WMO Climate Normals for LOS ANGELES/INTL, CA 1961–1990". National Oceanic and Atmospheric Administration. Retrieved 2014-04-17. 
  8. ^ "NCDC: U.S. Climate Normals". National Oceanic and Atmospheric Administration. Retrieved 2012-04-15. 
  9. ^ a b "Monthly averages for Santa Ana, California". Retrieved February 27, 2009. 
  10. ^ "Climatography of the United States No. 20 (1971–2000) - Culver City, CA" (PDF). National Oceanic and Atmospheric Administration. 2004. Retrieved 2010-07-25. 
  11. ^ "NCDC: U.S. Climate Normals". National Oceanic and Atmospheric Administration. 
  12. ^ http://climexp.knmi.nl/data/mgdcnUSC00045115.dat
  13. ^ http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?ca5115
  14. ^ http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?ca5114
  15. ^ http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?ca5082; http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?ca5085
  16. ^ a b "Pacific Ocean Temperatures on California Coast" - beachcalifornia.com