Forecasting the Weather and Storms 261 



tion, and yet extends upward but four 

 or five miles. The whole disk of whirl- 

 ing air four or five miles thick and i , 500 

 miles in diameter is called a cyclone or 

 cyclonic system. It is important that a 

 proper conception of this fundamental 

 idea be had, since the weather experi- 

 enced from day to day depends almost 

 wholly on the movement of these trav- 

 eling eddies, cyclones, or areas of low 

 pressure. 



That one may gain a clear under- 

 standing of the difference between the 

 movements of the air in the cyclone and 

 the movement of the cyclone itself, or 

 its translation from place to place, let 

 him picture in his mind the solar system, 

 with all of its planets and^their satellites, 

 turning each upon its own axis and 

 pursuing its orbit about the sun, and 

 then imagine the sun also as rotating 

 and as moving forward in space without 

 change in the relation of the planets to 

 the sun, or the satellites to the planets, 

 and he will have less difficulty in com- 

 prehending the various phases of the 

 translation of a cyclonic system and the 

 sequence in which the force and the di- 

 rection of the wind changes ; how the 

 wind must blow into the front of the 

 storm in a direction partly or wholly 

 contrary to the movements of the storm 

 itself and into the rear of the storm as 

 it passes away ; how the wind increases 

 in velocity as it gyrates spirally about 

 the center and approaches nearer and 

 nearer the region where it must ascend ; 

 how centrifugal force, in causing the 

 higher layers of air to move away from 

 the center, tends to cause an accumu- 

 lation of air about the outer periphery 

 of the storm, which in turn presses 

 downward and impels the surface air 

 inward. This whole complex system of 

 motion moves forward the same as does 

 the sun and his system. 



The black round disk indicates that 

 the weather is cloudy at the moment of 

 the observation, and the open disk clear 

 sky. S. and R. stand for snow and 



rain. The large figures in the four 

 quarters of the cyclone show the aver- 

 age temperature of each quadrant. The 

 greatest difference is between the south- 

 east and northwest sections. This is 

 due in part to the fact that in the south- 

 east quadrant the air is drawn north- 

 ward from warmer latitudes, and in the 

 northwest quadrant the air is drawn 

 southward from colder latitudes. 



Chart II, constructed from observa- 

 tions taken 12 hours later, shows that 

 the storm or cyclonic center, as indi- 

 cated by the word "low," has moved 

 from central Iowa since 8 a. m. and is 

 now, at 8 p. m., central over the south- 

 ern point of Lake Michigan. The 

 shaded areas show that precipitation has 

 occurred during the past 12 hours in 

 nearly the entire region covered by the 

 cyclone. Unfortunately for the science 

 of forecasting, precipitation does not 

 show that relation to the configuration 

 of the isobars that temperature, wind 

 velocity, and wind direction do. 



Note that none has fallen in the south- 

 ern portion of Ohio, in northwest Mis- 

 souri, and in West Virginia and eastern 

 Kentucky, although they are near the 

 storm center, while a fall has occurred 

 in New England, quite remote from the 

 center of barometric depression . These 

 facts illustrate how a forecast of rain or 

 snow may fail for a portion of a state or 

 for a whole state, even though the storm 

 pass over the state and the wind and 

 temperature change precisely as pre- 

 dicted. However, all the places men- 

 tioned as failing to receive precipitation 

 were showered upon during the further 

 progress of the storm, except northwest 

 Missouri, as will be seen by referring to 

 chart III of the following morning. 

 The cyclone has continued its course 

 toward the northeast, and has brought 

 the rain area eastward to include nearly 

 the whole Atlantic coast region. The 

 weather has cleared on the west side of 

 the storm. 



Charts II and III contain red lines, 



