72 STORMS AND WEATHER FORECASTS 



taken at the bottom of the ocean of air, storms suddenly de- 

 velop dangerous and unexpected energy or pursue courses not 

 anticipated in his forecast, or that the barometer at the center 

 of the storm rises without any premonition and gradually dis- 

 sipates the energy of the cyclonic whirl. 



These are a few of the generalizations of which the forecaster 

 takes cognizance and which guide him in his deductions. In 

 brief, he carefully notes the developments and movements in 

 the air conditions during the preceding 24 hours, and from the 

 knowledge thus gained he makes an empirical estimate of what 

 the weather will be in the different sections of the country the 

 following day. By preserving the weather charts each day and 

 noting the movements of the highs and the lows, any intelligent 

 person can make an accurate forecast for hiinself, always re- 

 membering that the lows, as they drift toward him from the west, 

 bring warm weather and sometimes rain or snow, and that as 

 they pass his place of observation the highs following in the 

 tracks of the lows will bring cooler and probably fair weather. 



We will now examine the accompanying charts and, after a 

 brief review of the Weather Bureau river service, will endeavor 

 to trace the inception and progression of the different classes of 

 storms. 



The stations from which the Weather Bureau issues and rap- 

 idly distributes forecasts and flood warnings are shown on Chart I. 

 Small radial lines are drawn to each central station from uj)- 

 river points in the various watersheds ; from these points daily 

 telegraphic measurements of rainfall and temperature are sent 

 to their respective centers, in addition to observations from 

 many of the full meteorological stations of the Bureau not 

 shown on this chart. 



With our many thousands of miles of navigable rivers flow- 

 ing through one of the most extensive and fruitful regions of 

 the world, daily forecasts of the height of water in the various 

 sections of each river are of enormous benefit to navigation, 

 and the warnings issued when the precipitation is so heavy aa 

 to indicate the gathering, during the next two or three days, of 

 flood volumes in the main streams, are often worth many mil- 

 lions to navigators and to those having movable property on 

 low grounds contiguous to the streams. 



The feasibility of making accurate forecasts as to the height 

 of water several days in advance at any station of the S3'stem is 



