USA > California > History of California, Volume V > Part 7
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THE CLIMATE OF CALIFORNIA
Icm., 0.4 inch, for every II meters, 36 feet, rise in elevation. The rate of increase is greatest about the 1,000-meter, 3,280-foot, level and becomes negative above the 2,000-meter, 6,562-foot level. At these high levels, however, much of the precipitation falls in the form of snow, and it is possible that with our present methods of reduction true values have not been obtained.
VARIATION OF RAINFALL WITH ALTITUDE
In the Monthly Weather Review, July, 1911, Charles Lee gives numerous diagrams showing the rate of increase of precipitation with elevation in various parts of California. Three sections of the Sierra Nevada are charted, the first known as the Central Pacific group, extending from Sacramento to Truckee; second, the Mokelumne section, extending from Stockton to Carson lake, about fifty miles south of the first group, and third, the Tuolumne group, extending from Merced to the southern end of Walker lake. The Fresno section then would constitute a fourth group, one still farther south. From all of them it appears that there is a definite increase in precipitation with elevation up to 1,500 meters, 5,000 feet, decreasing steadily above this. The average rate of increase is 8.5 inches, 215 millimeters, per 300 meters, 1,000 feet, 300 meters, up to 1,500 meters, 5, 000 feet.
East of the Sierra crest precipitation decreases rapidly with decrease in altitude, maintaining a con- stant rate to the 1,500-meter, 5,000-foot level and a decreasing rate below this elevation. The distance and precipitation curves conform to the profile in
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HISTORY OF CALIFORNIA
general shape, except that their maxima are west of the topographic crest, occupying the same relative position with respect to the Great Valley as the 1,500- meter, 5,000-foot level. They have a tendency to be- come horizontal over the level portion of the profile, to rise over western slopes below the 1,500-meter, 5,000- foot contour, to fall over western slopes above this, and to fall over eastern slopes. In other words, the general slope of the country seems to have more to do with the amount of precipitation than does altitude.
CENTRAL CALIFORNIA
The portion of California included under this head is bounded on the north by a line drawn from San Fran- cisco to Lake Tahoe; on the east by the Sierra Nevada; on the south by a line drawn from Point Conception south of Bakersfield and including the Fern watershed; and on the west by the Pacific.
The most prominent features are the bay of San Francisco, that portion of the great valley known as the San Joaquin, and the coast valleys, embracing the Santa Clara, the Salinas and other smaller valleys.
The bay of San Francisco is one of the great harbors of the world. While there is a continuous water passage from the Pacific ocean to the delta formed by the Sacramento and the San Joaquin rivers, the bay is locally considered as embracing only the central and southern portions of the water surface; the northern portion being known as San Pablo bay, which in turn is distinguished from Suisun bay lying to the east and connected with the former by the Straits of Carquinez. The length of the bay proper, in a northwest and south-
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THE CLIMATE OF CALIFORNIA
east line, is about forty-two miles; and the width varies from five to thirteen miles. At mean tide the area of the bay, exclusive of San Pablo and Suisun bays, is about four hundred and fifty square miles. The combined areas amount to about nine hundred square miles. The bay is connected with the Pacific Ocean by a narrow water passage varying in width from one mile to three miles and about six miles long. This is known as the Golden Gate. The city of San Francisco lies on the southern side of the Golden Gate, occupying the end of the peninsula, which is here about seven miles wide. The area occupied by the city amounts to about fifty square miles.
The climate of San Francisco is so out of the usual that it has attracted general attention .* There are certain noticeable features, such as the fogs and the low temperatures in midsummer, which are not found in such marked degree elsewhere. The climatic features of this city follow.
SUMMARIZED CLIMATIC DATA FOR SAN FRANCISCO
I. The monthly and annual mean temperature of the air. Jan., 49.2°; Feb., 51.3º; March, 52.1º; April, 53.8°; May, 55.7°; June, 56.3°; July, 56.4°; Aug., 57.0°; Sept., 59.1°; Oct., 58.5°; Nov., 55.2°; Dec., 50.2°; the annual, 56.6°.
2. The extent of the mean diurnal range of temperature for each month. Jan., 9.8°; Feb., II.0°; March, 11.6°; April, 12.9°; May, 12.2°; June, 13.3º;
*See McAdie, Climate of San Francisco, U. S. Weather Bureau Bulletin 44, 1913. Reed, W. G., The Rainfall of Berkeley, California, Univ. Calif. Publ. Geog., 1913, Vol. I, No. 2, pp. 63-79.
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July, 12.2°; Aug. 11.3°; Sept., 13.1º; Oct. 13.6°; Nov., II.4°; Dec., 9.8°. Annual, 11.8°. The greatest diurnal range, Jan., 24°; Feb., 25°; March, 27°; April, 33°; May, 35°; June, 43°; July, 31°; Aug., 38°; Sept., 41°; Oct., 33°; Nov., 26°; Dec., 22°. The greatest diurnal range for the entire period, 1871 to 1911, 43°. This occurred on June 29, 1891. The maximum was 100° and the minimum 57º.
3. The mean temperature at two specific hours, namely, the early morning and mid-afternoon. At 6 a. m. the mean temperature is, Jan., 46°; Feb., 48°; March, 49°; April, 50°; May, 51°; June, 52°; July, 53°; Aug., 54°; Sept., 55°; Oct., 55°; Nov., 52°; Dec., 47°; annual, 51°. At 3 p. m., Jan., 53°; Feb., 56°; March, 57°; April, 59°; May, 60°; June, 61°; July, 61°; Aug., 62°; Sept., 64°; Oct., 64°; Nov., 60°; Dec., 54°; annual 59°.
4. The extreme limits or total secular range of the' mean temperatures of the individual months: Jan., 54.8°-46.2°; Feb., 56.8°-47.8°; March, 57.2°-48.9°; Apri 58.2°-51.6°; May, 59.8°-52.6°; June, 62.4°-55.4; July, 61.6°-55.6°; Aug., 61.8°-56.4°; Sept., 64.6°-57.6°; Oct., 64.2°-56.6°; Nov., 59.0°-53.1º; Dec., 54.0°-47.0°.
5. The mean of the monthly and annual extreme temperatures and the resulting non-periodic range. Jan., 8.6°; Feb., 9.0°; March, 8.3º; April, 6.6°; May, 7.2°; June, 7.0°; July, 6.0°; Aug., 5.4°; Sept., 7.0°; Oct., 7.6°; Nov., 5.9°; Dec., 7.0°. The warmest year in 1890, with a mean annual temperature of 57.9°. The coolest year was in 1893, with a mean annual temperature, 54.3º, or an annual range of 3.6°.
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THE CLIMATE OF CALIFORNIA
6. The absolute highest and lowest temperatures that occur within a long interval of time. The absolute highest since 1871 is 101° on September 8, 1904; and the lowest 29° on January 15, 1888.
7. The mean variability of the temperature as expressed by the differences of consecutive daily means : These data are based upon records carrying six years, 1906 to 1911: Jan., 2.0°; Feb., 1.8°; March, 2.7°; April, 3.2°; May, 2.4°; June, 2.4°; July, 2.1º; Aug., 2.0°; Sept., 2.9°; Oct., 3.5°; Nov., 2.3°; Dec., 2.0°; for the year, 2.5°.
8. Mean limit or date of frost in spring and fall and the number of consecutive days free from frost.
During the past twenty years there has been no date when the minimum temperature of the air as officially recorded fell as low as 32°. Light frosts occur during the winter mornings, but no damage results.
9. The elements of solar radiation as measured by optical, chemical and thermal effects. No data available.
IO. The elements of terrestrial radiation as measured by radiation thermometers. No data available.
II. Temperature of the ground at the surface and to a depth of one or two yards. No data available. Records of street temperatures are obtained by a kiosk in Union Square park and also on Montgomery street, near California street. In general the range is greater than the official exposure gives. Temperatures 2° to 3° higher are recorded in the afternoon and 3º or 4° lower in the early morning.
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HISTORY OF CALIFORNIA
12. The monthly means of the absolute quantity of moisture in the atmosphere: Records covering one year, May, 1911, to April, 1912, give the following mean vapor tension, as determined from bi-hourly observations: Jan., .306 inch; Feb., .299; March, .266; April, .274; May, .290; June, .328; July, .365; Aug., .362; Sept., .364; Oct., .340; Nov., .283; Dec., .234; annual, .309 of an inch.
13. The monthly means of the relative humidity. The means as determined from 8. a. m. and 8 p. m. observations for 20 years, 1891 to 1910, are:
a. m.
p. m.
mean
January
87
75
81
February
86
72
79
March
85
70
77
April
80
69
74
May
86
71
78
June
89
77
83
July
92
82
87
August
93
79
86
September
88
73
80
October
86
71
78
November
85
71
78
December
84
73
78
Annual
87%
73%
80%
%
%
%
I4. The total precipitation, by monthly and annual sums. The annual precipitation, period 1850 to 1911, is 22.71 inches. The seasonal precipitation, i. e., from July Ist of one year until June 30, succeeding year, covering the seasons from 1849-50, to 1911-12, is 22.58 inches. The monthly amounts are Jan., 4.94;
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THE CLIMATE OF CALIFORNIA
Feb., 3.60; March, 3.35; April, 1.65; May, 0.72; June, 0.15; July, 0.02; Aug., 0.02; Sept., 0.30; Oct., 1.02; Nov., 2.55; Dec., 4.56.
15. The maximum precipitation per day and per hour. The heaviest precipitation on any one day occurred Jan., 28-29, 1881, from 11:08 p. m. 28th to II:08 p. m. 29th, amount 4.67 inches. The next greatest 24-hour rainfall occurred on September 24, 1904, when 3.58 inches fell. The heaviest hourly rainfall occurred on September 23, 1904, 0.97 of an inch fell. In two hours 1.29 inches fell and in 16 hours and 15 minutes, 3.58 inches fell.
16. The number of days having .of of an inch of precipitation, including dew or frost. The mean number of rainy days, period 1850 to 1911, Jan., II; Feb .; 10; March, II; April, 6; May, 4; June, I; July, o; Aug., o; Sept., 2; Oct., 4; Nov., 7; Dec., II; for the year, 67.
17. The percentage of rainy days in each month or the probability of a rainy day. Jan., 35%; Feb., 36%; March, 35%; April, 20%; May, 13%; June, 3%; July, o; Aug., o; Sept., 7%; Oct., 13%; Nov., 23%; Dec., 35%; for the year, 18%.
18. The number of days of snow with the depth and duration of the snow cover. Snow falls rarely in San Francisco. In the period of 41 years, 1871 to 1911, snow has fallen on 13 different dates. The greatest depth was 3.5 inches on December 31, 1882. The snow seldom lasts more than three hours. The longest duration was over night.
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HISTORY OF CALIFORNIA
19. The dates of earliest and latest snowfall: The earliest date was December 3Ist and the latest, March 3d.
20. Dates of earliest and latest hail: The earliest hail fell in October and the latest in May. Hail- storms are infrequent. In 20 years, 1891 to 1910, 56 hail-storms occurred. Forty-two of these occurred in December, January, February and March. None occurred in June, July, August and September.
21. Data regarding thunderstorms. Thunderstorms are rare, in a period of 20 years there have been 28 storms, eight of which occurred in one year. December is the month of maximum frequency. The storms are of short duration and feeble intensity. Damage from lightning is trivial.
22. The amount of cloudy sky, expressed in decimals. The period 1891 to 1910, Jan., 5.2; Feb., 5.0; March, 4.8; April, 3.8; May, 4.0; June, 3.3; July, 3.8; Aug., 4.2; Sept., 3.6; Oct., 3.4; Nov., 3.9; Dec., 4.4; annual, 4.1.
23. Percentage of cloudiness by monthly means for three or more specific hours of observation. Data not available.
24. Thickness of the cloud layer or the amount of strong sunshine as shown by candle sunshine recorder. Data not available.
25. Number of foggy days or total number of hours of fog. The number of foggy days recorded in period from 1891 to 1910, with one year missing, is 450, or an average of 24 days per year.
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THE CLIMATE OF CALIFORNIA
26. Number of nights with dew, also the quantity of dew. No records of nights with dew have been kept and there are no instruments for recording the amount of dew. In the afternoon and night fogs are accompanied by more or less condensation on the streets. This wetting is particularly noticeable on the south sidewalks, during the summer months from 6 p. m. until 9 a. m.
27. The monthly means or total wind velocities or estimated wind force. Period 39 years, 1872 to 1910, except December 40 years, and April and May, 1906, portions of month: Jan., 5,282 miles; Feb., 4,990; March, 6,563; April, 7,260; May, 8,416; June, 9,118; July, 9,494; Aug., 9,047; Sept., 7,156; Oct., 5,792; Nov., 4,649; Dec., 4,952; annual, 82,704 miles.
28. The frequency of winds from the eight principal points of the compass, and the frequency of calms. Jan., N., Feb., W .; March, W .; April, W .; May, W .; June, W .; July, W .; Aug. W .; Sept., W .; Oct., W .; Nov., W .; Dec., N .; annual, W. There are few calms and these occur chiefly in the winter months.
29. The frequency of winds for each hour of observation and the diurnal changes. The most frequent direction at I a. m. is W .; 2 a. m., W .; 3 a. m., W .; 4 a. m., W., changing to S.W .; 5 a. m., W-S.W .; 6 a. m., W .- S.W .; 7 a. m., W .- S.W .; 8 a. m., W .- S.W .; 9 a. m., W .- S.W .; 10 a. m., W .; II a. m., W .; Noon, W .; I p. m., W .; 2 p. m., W., 3 p. m., W .; 4 p. m., W .; 5 p. m., W .; 6 p. m., W .; 7 p. m., W .; 8 p. m., W; 9 p. m., W .; 10 p. m., W .; II p. m., W .; midnight, W. The diurnal changes are most noticeable during the
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HISTORY OF CALIFORNIA
winter months. In January the wind is south, from midnight until noon, veering to northeast from I p. m. to 3 p. m. and then becoming northwest. In February, the same change can be noticed except that the north- east winds begin at 9 a. m. and northwest at I p. m. During the late spring, the summer and fall the winds are steadily west. In November a shift to the south begins at 7 a. m., changing to northeast at 10 a. m., northwest at I p. m., and west at 3 p.m. In December the winds are light and variable from I a. m. until 3 p. m., mostly northeasterly. At 4 p. m. and through the balance of the day the winds are northwest.
30. Meteorological peculiarities of each wind direction, or the respective wind roses for temperature, moisture, cloudiness and rainfall. The north and northeast winds are accompanied by a higher tempera- ture in the summer and fall and lower temperature in winter. These winds are accompanied by low vapor content or dry weather, little cloudiness and light rainfall if any. The east, southeast, and south winds are accompanied by rising temperature, increasing moisture, considerable cloudiness and rainfall. The rain beginning some hours after the commencement of the wind. The southwest winds are accompanied by moderate temperature, much moisture, cloudiness and rain. The west and northwest winds are accompanied by a fall in temperature, moisture above the normal, much fog and little rainfall.
31. The mean annual barometric pressure. At sea level the annual pressure, mean of 38 years, 1873 to 19II, is 30.027 inches (762.5 millimeters), 1017 Kilobars.
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THE CLIMATE OF CALIFORNIA
32. Total evaporation, daily and monthly, or some equivalent factor, such as the depression of the dew- point, combined with the velocity of the wind. Data not available.
33. Variations in the gases contained in the atmosphere. Data not available.
34. Impurities in the atmosphere, such as the number of dust particles and especially the number of spores or germs of organic life. No data; but it is known that large amounts of carbon and sodium chloride exist in the air within a few hundred feet of the ground. The impurities are largely due to imper- fect combustion. Large quantities of smoke escape into the lower air. Fortunately the strong west winds carry the smoke and fog eastward over the water surface.
35. The proportions of ozone, peroxide of hydrogen and nitric acid. No data.
36. The electrical condition of the atmosphere. No data.
37. The sensation experienced by the observer, such as mild, balmy, invigorating, depressing, and other terms used to express the effect of the weather upon mankind. The climate is not mild or balmy; but rather invigorating, as a strong breeze from the sea stimulates. It may also be noted that the moderate temperatures are conducive to sleep and rest, especially during the summer. In this respect San Francisco differs from many of the great cities of the world. There is practically no period of the year when heat in any way interferes with the regular routine of life.
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HISTORY OF CALIFORNIA
38. The number of storm centers that pass over a given locality, or the storm frequency, monthly and annually. Comparatively few storms pass over San Francisco. During the summer months the mean path of storm movement is far to the north. During the winter months the relative frequency is three storms per month although in nearly every year there is a winter month without any marked disturbance. The spring months average two storms per month, the duration and intensity decreasing as the season advances.
39. Frequency of severe local storms. High southeast or southwest winds occur frequently during the winter months. During other months winds seldom reach a velocity of 40 miles. The relative frequency of severe local storms in which the winds exceed 50 miles an hour is about two each winter season. In the past 20 years there have been three occasions when the wind reached 60 miles or more, namely, November 30, 1906, 64 northeast; March I, 902, 60 south; December 23, 1892, 60 southeast.
40. The duration of twilight. There is less twilight than the normal for cities in latitude 37°to 38°, because summer afternoon fogs obscure the sky.
4I. The blueness or haziness of the sky. The skies are seldom as blue as in the mountain section. There is considerable haziness. Occasionally after a prolonged southeast storm, the air is remarkably pure and the visibility excellent.
42. The number and extent of sudden change from warm to cold or moist to dry weather and vice versa.
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THE CLIMATE OF CALIFORNIA
There are few sudden changes, and the climate is on the whole one of the most equable in the United States. The temperature range is small and the only marked changes occur during the periods of high temperature. Under such conditions the temperature falls suddenly in the afternoon of the second or third day, the wind changing to the west and the fog coming in from the sea.
43. In addition to the above we may add the one general factor of air drainage, or ventilation. San Francisco is one of the best ventilated cities in the world. A glance at the table of mean hourly wind velocities will show that there is a steady supply of fresh air, air from the ocean; and during the summer afternoons or in other words when most needed, the supply is greatest. This strong surface draught re- moves impurities, prevents stagnant conditions of the air, and the existence of poisonous gases. It also prevents colonization of mosquitoes.
The effect of the moderate temperature, high and nearly uniform amount of water vapor and excellent ventilation undoubtedly contribute to health.
One other fact should be noted, namely that there is little if any loss of sleep during the night hours. It is seldom if ever too warm during the summer nights and on the other hand seldom too cold for comfort on winter nights.
SAN JOAQUIN VALLEY
Regarding the general climatic features of the San Joaquin valley, it may be said that the precipitation is lower than might be expected. There is a practically rainless period from May to September. In some
106
HISTORY OF CALIFORNIA
seasons there are afternoon thunderstorms in the foot- hills and occasional light rains. The seasonal rainfall amounts to about ten inches in the central portion of the valley, and of this less than half an inch falls dur- ing the months of June, July, August, and September. The month of greatest rainfall is December, with an average of less than two inches. Notwithstanding the somewhat limited rainfall, the valley and foothill regions constitute the chief agricultural sections of the state. Apricots, cherries, almonds, walnuts, peaches, pears, plums, grapes, figs, and olives are grown most successfully. Citrus fruits of all kinds flourish in the foothill section. It may also be pointed out that this is the only section of the United States in which raisin- making is carried on.
The summer afternoon temperatures are exceedingly high. At Fresno a maximum temperature of 46℃, 115°F has been recorded; and temperatures of from 38° to 43℃, 100° to IIOºF are not unusual in the mid- summer months. Owing to intense radiation the diurnal range of temperature is large, the difference between the extremes frequently amounting to 20℃, 40ºF, or more. During the winter months the tem- perature falls to the freezing point or below. The lowest temperature recorded at Fresno was 7℃, 20ºF, on January 17, 1888. This was the coldest weather ever experienced in this section. Frosts occur fre- quently during the winter months; the first killing frosts occurring about the beginning of December, and the last about the end of March.
The prevailing winds are from the north and occasionally they are strong and do damage, especially
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THE CLIMATE OF CALIFORNIA
during the first part of June when the wheat is about ready for harvest. The summer days are as a rule cloudless. During the winter months, under certain pressure distribution, a low-lying land fog forms during the night and morning hours. This stratum of ground fog is not very deep, often not exceeding 30 meters, Ico feet, and is confined chiefly to the river courses and bottom lands. The foothill sections are for the most part above these winter fog belts.
SALINAS VALLEY
The next largest valley in central California is the Salinas valley, which lies west and southwest of the San Joaquin. Beginning at the mouth of the Salinas river, on the southern side of Monterey bay, the valley extends southeastward through Monterey and San Luis Obispo counties, nearly one hundred miles, with an average width of ten miles. On the west side of the valley the Santa Lucia range rises with an average altitude of 1200 meters, 4000 feet. On the east side, the valley is bounded by the various minor ranges forming the western boundary of the San Joaquin.
The coldest month is January and the warmest July. In the central part of the valley the mean annual rainfall is less than 400 millimeters, 15 inches. There are years, however, when the amount exceeds 500 millimeters, 20 inches, and, on the other hand, there have been two years in a period of thirty-seven when the annual rainfall did not exceed 175 millimeters, 7 inches. Both of these were unusually dry years in California. The rainfall is fairly well distributed for
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HISTORY OF CALIFORNIA
agricultural purposes. In the summer months strong north winds prevail; but from November to March the prevailing wind is south.
The city of Salinas has a mean annual temperature of 13℃, 56ºF. The highest temperature recorded was 36℃, 96°F, and the lowest 7℃, 20ºF.
The Santa Clara valley lies between the Santa Cruz mountains on the west and the Mount Hamilton range on the east. The prevailing westerly winds, intensified by the formation of the Golden Gate, are deflected up the Santa Clara valley as strong north winds. There are well-marked differences in temperature and rainfall between the valley and the coast. The mean annual rainfall at San Francisco is about 600 millimeters, 23 inches, and at San José about 400 millimeters, 15 inches. In other words, in going south a distance of fifty miles there is a steadily decreasing rainfall, amounting to about eight inches in the distance named. The Lick Observatory is situated on Mount Hamilton at an elevation of 1,283 meters, 4,209 feet above sea level. The station is about fourteen miles east of the city of San José. The mean annual precipitation is about 800 millimeters, 32 inches, or nearly double that of the floor of the valley. Rain falls in every month of the year on Mount Hamilton, but the summer rains are limited to light showers. More than half the annual rainfall occurs between December and March.
San José, the county seat of Santa Clara county, and most prominent city in the valley, lies fifty miles south of San Francisco and about eight miles south of the lower end of San Francisco bay. The elevation varies from 24 to 30 meters, 80 to 100 feet above sea level, but
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THE CLIMATE OF CALIFORNIA
within a few miles from the center of the city the foot- hills rise to heights exceeding 300 meters, 1,000 feet. The general movement of the air is from the north, and the valley is somewhat sheltered from the strong westerly winds prevalent on the coast. Summer fogs are not carried over the western hills, but hang in beau- tiful cascades along the ridge. There is a marked differ- ence in the amount of bright sunshine during summer afternoons between the valley, especially that portion near San José, and San Francisco. Low winter fogs sometimes occur, but as a rule do not last long.
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