GIFT OF DEPARTMENT OF AGRICULTURE THE UNITED STATES WEATHER BUREAU REPORT PREPARED FOR THE COMMISSION OF THE UNITED STATES OF AMERICA TO THE BRAZIL CENTENNIAL EXPOSITION For Distribution at the Brazil Centennial Exposition 1922-1923 WASHINGTON GOVERNMENT PRINTING OFFICE 1922 DEPARTMENT OF AGRICULTURE THE UNITED STATES WEATHER BUREAU Supplementing Exhibit of the UNITED STATES WEATHER BUREAU at the BRAZIL CENTENNIAL EXPOSITION Rio de Janeiro, Brazil 1922-1923 By DR. C. F. MARVIN Chief of the United States Weather Bureau - V THE -UNITED STATES WEATHER BUREAU. ljj6 risgulat' observing stations scattered throughout the United States, its Territories, and the West Indies, and upon similar reports received daily from points in other parts of the Northern Hemisphere. Each of the Weather Bureau stations is operated by one or more trained observers, and is equipped with mercurial barometers, thermometers, wind vanes, rain and snow gauges, anemometers, and sunshine recorders ; also barographs, thermographs, and other devices which make continuous automatic records of the local weather conditions. The results of the twice-daily observations are immediately telegraphed to the central office at Washington, D. C., and other forecast centers where they are charted for study and interpretation by experts trained to forecast the weather conditions expected during the following 36 to 48 hours. A complete telegraphic report includes the following data: Temperature, pressure (reduced to sea level), precipitation, direction and velocity of wind, kind of weather, clouds; and also maximum or minimum temperature since last observation. From these data the forecaster, by comparison with preceding reports, is able to trace the paths of storm areas from the time of their appearance to the moment of obser- vation and approximately determine and forecast their subsequent courses and the attendant weather conditions. Weather services are maintained by the Canadian and Mexican Gov- ernments, and by a system of interchange daily reports are received from a number of stations in those countries. Daily observations are also received from foreign sources so that the field represented by the daily reports extends over a considerable portion of the Northern. Hemi- sphere. By means of the extensive survey of atmospheric conditions afforded by these reports it is possible to forecast important weather changes for a week in advance with a fair degree of accuracy. The principal stations in the United States receive reports from a sufficient number of other stations to show the general weather condi- tions over a considerable portion of the country. DISTRIBUTION OF FORECASTS. Forecast centers are maintained at five different points in the United States. Within two hours after the morning observations have been taken the forecasts are telegraphed from these centers (see map) to about i, 600 principal distributing points, whence they are further dis- seminated by telegraph, telephone, radio, and mail. The forecasts are available to many millions of people within an hour of the time of issue. This system of forecast distribution is wholly under the supervision and mainly at the expense of the Government, and is in addition to and dis- tinct from the distribution effected through the press. During the past few years the rapid development of radio has made possible a much greater distribution of the daily forecasts than heretofore. THE UNITED STATES WEATHER BUREAU. 3 THE WEATHER MAP. Weather maps are printed at many Weather Bureau stations and mailed soon after the morning forecast is telegraphed. On this map the impor- tant features of current weather conditions throughout the country are graphically represented. The map also contains temperature, precipi- tation, and other data from observing stations, and in addition a brief statement of the main weather features presented. In order that all sections of the country may receive weather data, maps or bulletins con- taining the data in tabular form are issued from most of the larger sta- tions. The maps issued at Washington and other forecast centers con- tain detailed forecasts for the respective forecast districts, while other station maps and bulletins contain forecasts only for the localities in which they are distributed. OCEAN METEOROLOGICAL SERVICE. The ocean meteorological service aims to collect, through the coopera- tion of vessel masters and others, meteorological observations at sea. It provides blank forms for reporting these observations, collects and charts them, reduces them to average values, and prepares the results for pub- lication on the ocean Pilot Charts issued by the Hydrographic Office of the United States Navy. WEATHER INFORMATION BY RADIO. The recent development of radio has made possible the transmission of meteorological observations made by ships at sea to shore stations, thence by land lines to a central meteorological station. The Weather Bureau has organized a system of meteorological obser- vations on vessels navigating the coastal waters of the Middle and South Atlantic States, the Gulf of Mexico, and the Caribbean Sea, the primary object being to gain information of subtropical storms which occasion- ally traverse these waters. Observations are made on vessels and trans- mitted by radio to shore stations, thence to the central office of the Weather Bureau, where they are charted and used in making forecasts and warnings. A similar service is also maintained on the Pacific coast. Distribution of weather information, forecasts, and warnings is made daily through the cooperation of the radio service of the United States Navy and other interests. (See chart of distributing stations.) CLIMATOLOGICAL SERVICE. Although the regular observing stations, each representing about 15,000 square miles of territory, furnish sufficient data upon which to base the various forecasts, observations at many intermediate points are necessary before the climatology of the United States can be properly studied. This need has given rise to the establishment of an 1127922 2 4 THE UNITED STATES WEATHER BUREAU. important and interesting feature of the Weather Bureau in its Clima- tological Service, which is divided into 45 local sections, each section, as a rule, covering a single State, and having for its center a regular observing station. These centers each month collect temperature and precipitation observations from more than 4,500 cooperative and other stations, and each publishes a monthly and an annual summary, which gives a large amount of climatological data for its section. Throughout the year the section centers receive weekly reports of weather and crop conditions from numerous correspondents. The central office at Wash- ington prepares weekly a general summary of weather and crop condi- tions for the entire country, which is incorporated in "Weather, Crops, and Markets." During the growing season in the cotton, corn, wheat, sugar, rice, broom-corn, and cattle-producing sections, designated centers receive telegraphic reports of precipitation and daily extremes of temperature from substations in the various sections, for publication in bulletin form. (See exhibit charts, Special Services.) MOUNTAIN SNOWFAUv MEASUREMENTS. Several hundred stations are maintained in the elevated mountain regions of western United States for the purpose of obtaining precise measurements of the depth and water content of the snowfall. Such measurements are useful in determining approximately the amount of water available for irrigating and power purposes. FORESTS AND STREAM FU>W. A special study to determine the effects of forest cover on the flow of streams is being made at Wagon Wheel Gap, State of Colorado, in co- operation with the Forest Service. Measurements of meteorological conditions and of stream discharge in two forested watersheds have been made during a period of nearly 10 years. The relation between the two streams having been established for forested conditions, one of the watersheds was denuded and the studies continued in 1920. The result- ing change in the relation between the streams will be a measure of the value of a forest as a controlling factor in run-off. AEROIvOGICAL INVESTIGATIONS. Free-air observations in the United States are made by means of kites and pilot balloons. The kites carry meteorographs which record pressure, temperature, humidity, and wind at all heights reached. The pilot balloons are inflated with hydrogen and released, and their move- ments through the air are followed by means of theodolites. The ob- served readings of these movements, together with the known height of the balloon, make possible the determination of wind direction and velocity at various altitudes. THE UNITED STATES WEATHER BUREAU. 5 The results of these observations are telegraphed to District Forecast Centers, where they are used in preparation of forecasts for aviators. (See Flying Forecast map.) The observations themselves are later forwarded by mail to the central office at Washington, D. C.. where they are computed, summarized, and studied. SPECIAL PUBLICATIONS. Among the publications of the Weather Bureau the following are worthy of special notice: (a) The annual report of the chief of bureau, including a full summary of climatic data for the United States. (6) The Monthly Weather Review, which contains elaborate meteor- ological tables and charts showing the weather conditions for the month over the United States and neighboring countries and papers of unusual interest on climatological and meteorological subjects. (c) Climatological data for the United States and territories, con- sisting of monthly and annual summaries mostly by States, and con- taining charts and daily climatological statistics of temperature and precipitation for the entire country. (d) A vast amount of climatological data has been prepared in a series of separates, each treating of the principal climatic features of a limited area, the complete set, 106 hi all, covering the entire United States. (e) The bulletins and Weather Review supplements, published occa- sionally and now numbering about 70, that contain the larger reports along special lines made by the experts of the service. INSTRUMENTS AND APPARATUS. Accurate observations of temperature, rainfall, and atmospheric pressure, etc., are possible only by aid of suitable instruments properly exposed. The kites, meteorographs, self -registering instruments, and other forms of apparatus devised by the Weather Bureau are known throughout the world. The present perfected equipment has been obtained through constant endeavor extending over a period of nearly 50 years. APPLICATIONS OF FORECASTS AND WARNINGS. The extent to which the work of the Weather Bureau affects the daily life of the people and becomes a factor in their various vocations and business enterprises, already very great, is increasing yearly. Warnings of storms and hurricanes, issued for the benefit of marine interests, are the most important and valuable. Storm warnings are displayed at more than 300 points along the Atlantic, Pacific, and Gulf coasts and the shores of the Great Lakes, including every port and harbor of any considerable importance ; and so nearly perfect has this service become that scarcely a storm of marked danger to maritime interests 6 THE UNITED STATES WEATHER BUREAU. occurs for which ample warnings are not issued from 12 to 24 hours in advancer The reports from the West Indies are especially valuable in this connection, as they enable the bureau to forecast with great accuracy the approach of those destructive hurricanes which, during the period from June to November, are liable to sweep the Gulf and Atlantic coasts. Warnings of sudden and destructive temperature changes known as cold waves are probably next in importance. They are issued from 24 to 36 hours in advance of the cold wave, and disseminated throughout the threatened regions by all the means quickly available. Warnings of frosts and freezing weather are also of immense value, particularly to the fruit, sugar, tobacco, cranberry, and market gardening interests. The truck-raising industry so extensively carried on in the regions bordering on the Gulf and lower Atlantic coasts and which has increased so greatly in recent years, is largely dependent for its success on the cooperation of the Weather Bureau. In the citrus-fruit districts of California fruit with an estimated value of $14,000,000 was saved by taking advantage of warnings issued by the bureau during one cold wave. In other fruit districts growers rely largely upon the warnings of the bureau to guide them in smudging and heating their orchards on the occurrence of frost or freezing weather during the blossoming period. RIVER AND FLOOD SERVICE. Human life and large property interests along the rivers of the United States are safeguarded by the issue of flood warnings. The river and flood service is organized with its principal headquarters at Washington, D. C., and subsidiary district centers at advantageous points on the respective rivers along which a service is maintained. Measurements of precipitation on the headwaters of the streams and observations of the height of water on the gage at upstream points are collected by telegraph or telephone from substations and serve as the basis for warnings of floods in the lower reaches of the streams. Another useful purpose is served on navigable streams giving notice of boating stages during the low-water season. OTHER BENEFITS DERIVED FROM REPORTS AND WARNINGS. While the value of the bureau's assistance to many interests is so obvious as scarcely to need more than the brief mention already given, there are numerous special applications that might not have been sus- pected, a few of which may well be noted here. The railway and transportation companies make continued use of the forecasts in all of their shipments. Perishable products are protected against temperature extremes by icing or heating, as conditions may require. Shipments of perishable goods are accelerated when it is THE UNITED STATES WEATHER BUREAU. 7 found possible to carry them to their destination in advance of the expected unfavorable temperature conditions, or they may be delayed to prevent loss. The uses made of temperature forecasts in the cities are more varied than is generally supposed. With notice of an approaching cold wave preparations are made by heating and lighting plants to meet the in- creased demands that will follow. Plumbing is protected. Street rail- way companies arrange for more heat in their cars. Merchants curtail advertisements or direct attention largely to cold-weather articles. Ice factories reduce their output. Charity organizations prepare to meet increased demands for food and fuel, and thus minimize suffering among the poor. Frost warnings are utilized in the cranberry regions by flooding the bogs until after the cold weather has passed or danger of frost is over. Many crops are saved by being harvested in advance of the freeze. Rain forecasts are utilized to enable picking or harvesting of fruit or other crtfps to be done in advance of rains. City departments determine the number of teams needed in street sprinkling; railroad companies guard against washouts; and irrigation companies control the output of water by expected conditions of rainfall as given in the forecasts. Warnings of heavy snows are valuable to railroads by enabling them to organize their snow-fighting equipment and to possibly reduce the tonnage of their freight and passenger trains. On the great western ranches and plains, stock is hurried from the ranges to shelter upon notice of blizzards, northers, or heavy snows. Some special uses of the storm warnings are found in the measures adopted to protect property and crops subject to inundation from high tides or backwater blown up by the winds. Vessels load hurriedly to get off in advance of unfavorable winds. Flood warnings are indispensable to river industries, and to operations carried on in lowlands subject to inundation. Their issue is followed by the removal of cattle from bottom lands and by the saving of such crops as can be cut before the high water reaches, a threatened district. Along the river streets of many cities the basements of warehouses and other buildings are submerged at high water; accurate river forecasts enable the business men to postpone moving their goods to the upper floor until the last moment, and often prevent the needless expense of such a transfer in cases where it is known that the flood crest will be below the point at which basement stock would be imperiled. The daily maps and bulletins and the general bulletins and reports containing statistical data are utilized in many ways by the public. Grain and cotton brokers are guided largely by the forecasts in their operations. Statistics of wind pressure and direction are issued in the design of high buildings and to determine the origin of fires resulting from flying sparks. Humidity records are used by silk and candy manu- 8 THE UNITED STATES WEATHER BUREAU. facturers, in tuberculosis investigations, and in studies of the loss of electric current in high voltage transmission. Data regarding rainfall and snowfall are extremely useful in planning irrigation enterprises and selecting reservoir sites, and are studied in connection with the construction of water works, bridges, culverts, and sewers. Climatological data are used in scientific studies of the relation of weather to health, life, and human pursuits ; by railroad companies in the adjustment of claims and demurrage charges; by homeseekers; by inva- lids in search of health resorts; by irrigation investigators; by contractors and builders in settling labor accounts; by merchants in studies of the relation of the weather to their daily sales; as adequate testimony in court proceedings; in dry-farming investigations; in studies of soil culture, practical agriculture, and the life and migration of insect pests; in plans for the development of the arid regions; in the preparation of historical records; by bond and investment companies in determining the loan values of farm lands in newly opened countries ; in short, in nearly every calling in which the weather plays any part. THE EXHIBIT. The charts and pictures are arranged according to the following plan: In the center are shown the means by which weather reports are col- lected and the forecasts distributed, the radio being featured. Copies of charts actually used in forecast work are exhibited. Four additional groups of charts and pictures illustrate the character of the principal services. In the upper right-hand corner the river and flood service, below that the special services ; in the upper left-hand cor- ner, the use of the general wind and weather forecast, below that the storm-warning and hurricane service. Other groups indicate the nature of the aerological and the instrument work; and for general interest there are cloud charts, illuminated pic- tures, climatological charts, and maps showing storm movements. LD 21-100m-12,'43 (8796s) 493810 UNIVERSITY OF CALIFORNIA LIBRARY