WEATHER BUREAU 



6231 



WEATHER BUREAU 



U S. Department of Agriculture 

 WEATHER BUREAU 



A DAILY MAP PUBLISHED BY THE WEATHER 



a low-pressure area cloudiness is the prevail- 

 ing condition, while a high-pressure area is 

 characterized by clear skies. To the forecaster 

 the barometer reading is of as much impor- 

 tance as all of the other information com- 

 bined, for the pressure of the air is the pri- 

 mary element in the study of all atmospheric 

 movements. The chart also contains dotted 

 lines called isotherms. These pass through 

 points of equal temperature and are drawn only 

 for freezing and zero. 



By means of these weather maps a forecaster 

 can predict conditions not only for his own 

 locality, but also for those of states and cities 

 at a distance. The forecasting centers are 

 Washington, Chicago, New Orleans, Denver, 

 San Francisco and Portland, Ore. From these 

 centers over 2,050 Weather Bureau stations and 

 forecast distributing centers receive daily re- 

 ports, which arc in turn sent by telephone and 

 iph to more than 5,465,000 patrons, while 

 120,050 places are reached through regular mail 

 routes and rural free delivery. Predictions are 

 made of weather conditions for thirty-six to 

 eight hours in advance. 



In addition to the weather charts c< 

 the United States, the central office prepares 

 each morning a chart of pressure and v. 



conditions over the entire northern hemisphere, 

 based on reports received from meteorological 

 bureaus in Europe and Asia, and from Weather 

 Bureau stations in the United States, Alaska, 

 Hawaii and the West Indies. Wireless mes- 

 sages containing weather information come 

 from the Aleutian Islands of Alaska, and cabled 

 reports are received daily from Nemuro, in 

 Japan, and from Shanghai, in China. By means 

 of these various channels of information the 

 central office is qualified to predict general 

 weather and temperature conditions ov 

 entire United States for a week in advance. 

 In the summer of 1916 the violence and dura- 

 tion of the hot period that caused so much 

 suffering throughout the Middle West were 

 forecast with remarkable accuracy. 



The Bureau also sends out special warnings 

 in regard to weather conditions by means of a 

 system of flags and signals, such as arc illus- 

 trated in this art 



River and Flood Division. This branch of the 

 service has been the means of saving many 

 lives and millions of dollars' worth of property 

 through its warnings of floods, especially in the 

 Ohio and the Mississippi valleys. It also 

 maintains stations for the measurement of snow- 

 fall in the mountain regions of the West, with 



