Climate of San Diego

San Diego
Climate chart (explanation)
J F M A M J J A S O N D     1.8   66 49     1.5   67 51     1.8   66 53     0.8   68 56     0.2   69 59     0.1   72 62     0   76 66     0.1   78 67     0.2   77 66     0.4   75 61     1.5   70 54     1.6   66 49 Average max. and min. temperatures in °F Precipitation totals in inches Source: WMO
Metric conversion J F M A M J J A S O N D     46   19 9     39   19 10     45   19 12     20   20 13     4.8   21 15     1.8   22 17     0.5   25 19     2.5   25 20     6.1   25 19     9.4   24 16     37   21 12     40   19 9 Average max. and min. temperatures in °C Precipitation totals in mm

The Climate of San Diego, California is categorized as Semi-arid climate|semi-arid or Mediterranean climate|Mediterranean] (Köppen climate classification BSh or Csa/Csb). It enjoys mild, sunny weather throughout the year. Since the San Diego area straddles areas of Mediterranean climate (CSa) to the north, and Semi-arid climate (BSh) to the south and east, it is often referred to as "Mediterranean" or "arid-mediterranean".^[1]

Temperatures

Average monthly temperatures range from 57.3 °F (14.1 °C) in January to 72.5 °F (22.5 °C) in August, although late summer and early autumn are typically the hottest times of the year with temperatures occasionally reaching 90 °F (32 °C) or higher.^[2] Snow and ice are rare in the wintertime, typically occurring only inland from the coast when present. "May gray and June gloom", a local saying, refers to the way in which San Diego sometimes has trouble shaking off the fog that comes in during those months. Temperatures soar to very high readings only on rare occasions, chiefly when easterly winds bring hot, dry air from the inland deserts (these winds are called "Santa Ana winds").

The record high temperature at the National Weather Service office in San Diego of 111 °F (44 °C) was on September 26, 1963. The record low temperature was 25 °F (−4 °C) on January 7, 1913.^[3]

Precipitation

San Diego has on average 146 sunny days and 117 partly cloudy days a year. The average annual precipitation is less than 12 inches (300 mm), resulting in a borderline arid climate. Rainfall is strongly concentrated in the cooler half of the year, particularly the months December through March, although precipitation is lower than any other part of the U.S. west coast. The summer months are virtually rainless. Rainfall is highly variable from year to year and from month to month, and San Diego is subject to both droughts and floods. Hurricanes and thunderstorms are very rare. Coastal areas are driest; Cleveland National Forest receives more precipitation, and some inland areas like Laguna Mountains average more than 30 inches of rainfall per year.

At the National Weather Service office, there are an average of 43 days with measurable precipitation. The wettest year was 1941 with 24.93 inches (63.3 cm) and the driest year was 1953 with 3.23 inches (8.2 cm). The most rainfall in one month was 9.09 inches (23.1 cm) in January 1993. The most rainfall in 24 hours was 3.23 inches (8.2 cm) on April 5, 1926.^[4]

Snow

Snow has been recorded falling on San Diego communities only five times in over 125 years of record-keeping.^[5] Snow flurries were last seen in San Diego on February 15, 2008 around 1,700 to 1,800 feet (520 to 550 m), and the last measurable snowfall to hit various neighborhoods and suburbs around the city fell on December 13, 1967. In winter, light snow is common in mountainous regions of east San Diego County above 3,000–4,000 feet (910–1,200 m).^[6]

Variation

Climate in the San Diego area often varies dramatically over short geographical distances, due to the city's topography (the Bay, and the numerous hills, mountains, and canyons), thus exhibiting microclimate: frequently, particularly during the "May gray / June gloom" period, a thick "marine layer" cloud cover will keep the air cool and damp within a few miles of the coast, but will yield to bright cloudless sunshine between about 5 and 15 miles inland—the cities of El Cajon and Santee for example, rarely experience the cloud cover. This phenomenon is known as microclimate.

Compared to National Averages

On average San Diego sees 41 days with some precipitation while the rest of the country sees about 110. The national average for mostly sunny days is 213 while San Diego's is 267. San Diego's annual snowfall is 0 inches per year while the nation usually sees an average of 24.2 inches (610 mm) per year. The United States average for days above 90 °F (32 °C) is 37.9 days while San Diego's is only 2.5 days, and there are, on average 0 days below 32 °F (0 °C) in San Diego, while the national average is 88 days. The average low temperature in January for the country is 26.5 °F (−3.1 °C), and for San Diego it is 50 °F (10 °C). The average high temperature in July for San Diego is 76 °F (24 °C). The national average is 86.8 °F (30.4 °C).^[7]

Monthly Averages

Climate data for San Diego (San Diego Airport)
Month	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Average high °F (°C)	65.8 (18.8)	66.3 (19.1)	66.3 (19.1)	68.7 (20.4)	69.3 (20.7)	72.2 (22.3)	75.8 (24.3)	77.5 (25.3)	77.0 (25.0)	74.0 (23.3)	69.9 (21.1)	66.3 (19.1)	70.8
Daily mean °F (°C)	57.8 (14.3)	58.9 (14.9)	60.0 (15.6)	62.6 (17.0)	64.6 (18.1)	67.4 (19.7)	70.9 (21.6)	72.5 (22.5)	71.6 (22.0)	67.6 (19.8)	61.8 (16.6)	57.6 (14.2)	64.4
Average low °F (°C)	49.7 (9.8)	51.5 (10.8)	53.6 (12.0)	56.4 (13.6)	59.8 (15.4)	62.6 (17.0)	65.9 (18.8)	67.4 (19.7)	66.1 (18.9)	61.2 (16.2)	53.6 (12.0)	48.9 (9.4)	58.1
Rainfall inches (mm)	2.28 (57.9)	2.04 (51.8)	2.26 (57.4)	0.75 (19.1)	0.20 (5.1)	0.09 (2.3)	0.03 (0.8)	0.09 (2.3)	0.21 (5.3)	0.44 (11.2)	1.07 (27.2)	1.31 (33.3)	10.77 (273.6)
Avg. rainy days (≥ 0.01 in)	7.2	6.6	7.2	4.1	2.0	1.1	0.6	0.6	1.5	2.8	4.0	5.2	42.9
Sunshine hours	238.7	228.8	260.4	276.0	251.1	243.0	303.8	294.5	252.0	244.9	231.0	232.5	3,056.7
Source no. 1: NOAA (1971-2000) [8]
Source no. 2: HKO (sun, 1961-1990) [9]

Santa Anas

The months of September through February bring warm winds from the desert that are called, "Santa Anas". Occurring about 10 days out of the year, these winds bring sometimes hot, but always dry conditions. Inland, and in mountain passes and canyons, they can burst out in gusts of 100 miles per hour (160 km/h) and can lower relative humidity to single digits, although by the coast they rarely see gusts of over 40 miles per hour (64 km/h). They can spread and worsen wildfires. Because these winds blow from east to west, common perception is that they are pulling hot air from the desert. However, it is not uncommon during a Santa Ana condition for the coast to be even hotter than the desert regions. The Santa Ana winds are actually warm due to barometric pressure increases: as the air is pulled down to sea level from the higher altitudes of the Great Basin and Rocky Mountains to the east it compresses and heats up.^{[citation needed]}

Hurricanes

See also: List of California hurricanes

San Diego is only 3° further north than New Orleans, and technically within reach of East Pacific hurricanes. However, cold California Current off the coast of California keeps ocean water significantly colder than in the Gulf of Mexico and western Atlantic. As a result, virtually all northbound hurricanes dissipate over Baja California and fail to bring any precipitation to San Diego. The only tropical cyclone known to impact San Diego as a hurricane in around 200 years of record-keeping was the 1858 San Diego Hurricane. Two more cyclones managed to bring tropical storm-force winds to Southern California: the 1939 California tropical storm and the Hurricane Kathleen (1976).

May and June clouds

During the months of May and June, a common natural occurrence brings a thin layer of clouds that covers coastal and inland communities. Some call it "May Gray", or "June Gloom."

See also

• Climate of California

References

1. ^ M. Kottek; J. Grieser, C. Beck, B. Rudolf, and F. Rubel (2006). "World Map of the Köppen-Geiger climate classification updated". Meteorol. Z. 15: 259–263. doi:10.1127/0941-2948/2006/0130. http://koeppen-geiger.vu-wien.ac.at/pics/kottek_et_al_2006.gif. Retrieved April 22, 2009. 
2. ^ National-Record High Temp: http://www.met.utah.edu/jhorel/html/wx/climate/hitemp.html
3. ^ http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?ca7740; http://www.city-data.com/forum/weather/155963-your-record-high-record-low-10.html
4. ^ http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?ca7740
5. ^ "Rowe, P.: "The Day it Snowed on San Diego" San Diego Union-Tribune, December 13, 2007.
6. ^ "Snow play" a popular winter activity at at Laguna Mountain Recreation Area and Cuyamaca Rancho State Park (Feb 26 2011)
7. ^ http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?ca7740
8. ^ "Climatography of the United States No. 20: San Diego Lindbergh AP, CA (1971–2000)" (PDF). National Oceanic and Atmospheric Administration. 2004. http://cdo.ncdc.noaa.gov/climatenormals/clim20/ca/047740.pdf. Retrieved 2010-05-31. 
9. ^ "Climatological Normals of San Diego". Hong Kong Observatory. http://www.hko.gov.hk/wxinfo/climat/world/eng/n_america/us/san_diego_e.htm. Retrieved 2010-05-12. 

External links

• USTravelWeather.com: San Diego Weather and Climate