File:San Francisco water (1925) (14781419564).jpg

Identifier: sanfrancwat4192581930spri (find matches)
Title: San Francisco water
Year: 1922 (1920s)
Authors: Spring Valley Water Company (San Francisco, Calif.)
Subjects: Water-supply
Publisher: San Francisco, Calif. : Spring Valley Water Co.
Contributing Library: San Francisco Public Library
Digitizing Sponsor: California State Library Califa/LSTA Grant

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meter falls steadily, a storm is ap-proaching from the west or northwest, and itscenter will pass near or north of the observer with-in 12 or 24 hours with wind shifting to northwestby way of southwest and west. When the windsets in from points between east and northeast andthe barometer falls steadily, a storm is approach-ing from the south or southwest, and its center willpass near or to the south or east of the observerwithin 12 or 24 hours with the wind shifting to thenorthwest by way of north. The rapidity of thestorms approach and its intensity will be indicatedby the rate and the amount of the fall in thebarometer. Weather forecasts are made daily by theUnited States Weather Bureau, based on ob-servations of barometric pressure, tempera-ture, wind, humidity, rain, and sunshine, ata great number of stations scattered over theUnited States and Canada, and from shipsat sea. These observations are made at 8 a.m.and 8 p.m. 75th-meridian time, which is SAN FRANCISCO WATER April, 1926
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Figure i. U. S. Daily Weather Map for Monday, February I, 1926, showing center of approaching storm, about 1700miles northwest of San Francisco. Heavy broken lines are drawn through points of same barometric pressure 5 a.m. and 5 p.m. Pacific time, and the in-formation is transmitted by telegraph andradio to Washington and other cities whereforecasting stations are located. These data are transferred to a base map.On this map one set of lines is drawn throughpoints of equal barometric pressure, and an-other set drawn through lines of equal tem-perature. The former lines are called iso-bars, and the latter isotherms. These linesshow the location of all the areas of high andlow barometric pressures, and are indicatedon the maps as High and Low. (SeeFigures 1 and 2.) After the map is com-pleted the forecaster, from long experienceand intimate knowledge, makes his forecastfor the next twenty-four to thirty-six hours.The maps with the forecasts are then printedand quickly distributed to th

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