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No feature of San Diego is better worthy of a place in these historical records than the famous climate which, of all local resources, is the one which has done most to create the city and give it wide reputation. It is a pity that exact information does not go back to the time of the earliest settlement. Of the Mission period we have only such meager records as this kept by the Fathers at San Luis Rey:
1776, Copius rainfall.
1787, Rain insufficient, crops short.
1791, Extremely dry. No rain the whole year.
1794, Rainfall insufficient, crops short.
1795, Very dry.
1819, Short in rain and crops.
1827, Short in rain and crops.
1832, Short in rain and crops.
This would seem to be an effectual answer to the saying of the Spaniards that drouth was unknown until the Americans came. Fortunately, we do not depend upon such fragmentary records for the history of the climate in later times. The facts in this chapter are supplied by the U. S. Weather Bureau forecaster, Ford A. Carpenter, and are given in his own words:
Ford A. Carpenter
Local Forecaster U.S. Weather Bureau. Located, 1896; having been transferred from Carson, Nevada. Promoted in 1906 to Local Forecaster; since 1892, Director of San Diego Natural History Society; since 1905, Director of Chamber of Commerce, and now Treasurer of same. First President of San Diego Camera Club |
Four elements enter into a consideration of the climate of San Diego. Named according to their importance, they are as follows: (1) Distance from the northern storm tracks, and the southern storms of the Lower California coast; (2) proximity to the ocean on the west; (3) mountains in the east, (4) and the great Colorado desert still further east. The number of the northern areas of low pressure sufficiently great, and moving far enough south to exert an influence at the latitude of San Diego, are comparatively few; not one-tenth of these lows have an appreciable effect on the climate. The storms from the south ("Sonoras," as they are locally known), have but little energy, and probably average two a year. As is the case in all marine climates the ocean exerts by far the most powerful effect. This is noticed in the slight daily variation in temperature, and the absence of either cold or hot weather. The average daily change in temperature from day to day is 2 degrees, and the extremes in temperature, from a record of thirty-four years, are 101 degrees and 32 degrees. The temperature has exceeded 90 degrees twenty-two times in thirty-four years, or on an average of about twice every three years. Five times in the history of the station has the temperature touched 32 degrees, but has never fallen lower. Five killing frosts have occurred in San Diego since the establishment of the station, but aside from blackening tender shoots, and killing delicate flowers, no damage was done.
The "desert" winds are responsible for temperatures above 90 degrees, and they are therefore accompanied by extremely low humidity. Records of humidity below 10 per cent are not uncommon during the two or three hours duration of the desert wind; 3 per cent is the lowest relative humidity ever recorded at this station. As the sea-breeze is stronger than the desert wind, the highest point reached, whenever the temperature is above 90 degrees, usually occurs about eleven a.m. At this time the sea-breeze overcomes the land-breeze, and the temperature drops to the normal.
Rain Map of California |
Nothing so clearly illustrates the strictly local character of the climate of San Diego as the humidity. While the mean annual relative humidity is 72 per cent at the Weather Bureau station, two miles north and at an increase of two hundred feet in elevation, the humidity decreases 15 per cent. Five miles away, and at an elevation of three hundred feet, there is a further decrease of 5 per cent. The temperature is of course proportionately higher.
The maximum amount of sunshine occurs in November, and the minimum in May and June; the winters being usually bright and warm, and the summers cloudy and cool The photographic sunshine recorder was installed in 1890, and this sixteen years record shows an average of about three days each year without sunshine.
In 1902, there were two days above 80 degrees and three days below 40 degrees, making 9,905 days out of a possible 10,226 days since 1875 (inclusive), when the temperature did not go beyond these extremes.
Rainfall Chart of San Diego County |
In 1903, there were seven days above 80 degrees and 7 days below 40 degrees, making 9,919 days out of a possible 10,591 days, since 1875 (inclusive), that the temperature did not go beyond these extremes.
In 1904 there were 21 days above 80 degrees and one day below 40 degrees, making 10,262 days out of a possible 10,956 days since 1875 (inclusive), that the temperature did not go beyond these extremes.
In 1905, there were seven days above 80 degrees and three days below 40 degrees, making 10,608 days out of a possible 11,321 days.
There is a difference of about one mile an hour in the average hourly velocity of the wind between the summer and the winter months; the mean annual hourly velocity is five miles. While the wind blows from every point of the compass during a normal day, the land-breeze is very light, averaging about three miles per hour, reaching its lowest velocity just before the seabreeze sets in. The records show that there is an average velocity of from six to nine miles from ten a.m. to six p.m. During the summer a velocity of six miles is attained at nine a.m., increasing to ten miles at two p.m., reaching six miles at seven p.m.
The winter months have about five hours of moderate wind beginning shortly after noon. Winds from twenty-five to thirty miles per hour occur infrequently, the average annual number being two. Winds of from thirty-one to forty miles have an average of less than one a year. The highest velocity ever attained was forty miles from the northwest, in February, 1878.
The record of meteorological observations began in July, 1849, and was made entirely by officials of the Government. The Army and Coast Survey kept up the record until the establishment of this station by the Signal Service, Nov. 1, 1871. Since this date, the location of the observing office has been changed a number of times, but the different places have all been within a radius of a few blocks. The office is now in the Keating building, corner Fifth and F streets. The instruments have elevations above ground as follows: thermometer 94 feet; rain-gage, 86 feet; anemometer, 102 feet.
[from William Ellsworth Smythe's History of San Diego, 1908, pp. 675-686]
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