Forecasting the Weather and Storms 



297 



developing the ■ normal storm tracks ' for 

 a given locality. In this figure, drawn to 

 to the scale of the Washington weather 

 map, the vector X represents the direc- 

 tion and movement in 24 hours of the 

 storm that was centered near Amarillo, 

 Texas, 8 a.m., May 26, 1903. The vector 

 is the resultant of the pressure acting 

 from the north, northeast, east, etc., in 

 the direction indicated, and was deter- 

 mined from an increase in pressure from 

 the storm center outward at 8 a.m., May 



Chart XVI — Showing method followed in developing 

 normal storm tracks and in ascertaining the correct 

 value to represent the pressure exerted on a storm 

 center that causes it to depart from a normal track. 



26, as follows : To the north, o. 10 inch ; 

 northeast, o 00 ; east, 0.60 ; southeast, 

 0.30; south, 0.30; southwest, 0.30; 

 west, 0.30, and northwest, 0.20, each 

 tenth of an inch being given a value of 

 one centimeter. The vector Y repre- 

 sents the 24-hour movement of the 

 storm that was centered over Amarillo, 

 Texas, at 8 a. m., May 28, 1903. The 

 vector Yj is the resultant of the pressure 

 exerted on the storm center, determined, 

 as above, from an increase in pressure 

 from the storm center toward the several 



directions, as follows : To the north , o. 30 

 inch ; northeast, o. 20 ; east, 0.60; south- 

 east, 0.30 ; south, o. 10 ; southw T est, o. 10 ; 

 west, o. 10, and northwest, 0.40. 



" The vector X being the resultant 

 of the forces that propelled the storm 

 in the direction and to the point indi- 

 cated in 24 hours, it is possible to elim- 

 inate the pressure influence (if it be 

 given an appropriate value) by resolv- 

 ing the vector representing the track of 

 the storm into its two components, one 

 of which, Xj, being the result- 

 ant of the pressure exerted on 

 the storm, the other, X 2 , will 

 represent the 24-hour value that 

 should be given the general 

 circulation of the atmosphere 

 that carried the storm with it. 

 Similarly, Y 2 represents the 24- 

 hour value that should be given 

 the general circulation that car- 

 ried the storm of May 28 with 

 it. It will be observed that X 2 

 and Y 2 , representing the 24- 

 hour values of the general cir- 

 culation on the two dates, are 

 of equal length and vary not 

 more than 3 degrees 30 min- 

 utes in direction, from which 

 it may be assumed that the 

 general circulation of the at- 

 mosphere in May that carries 

 the storms of the region of New 

 Mexico and northwest Texas 

 with it may be represented by 

 a mean of a number of vectors 

 determined as above. It is manifest, 

 therefore, that should a storm in May 

 in the region indicated be acted upon 

 by a distribution of pressure whose 

 resultant is zero its 24-hour direction 

 and rate of movement will be that of the 

 general circulation represented by a cor- 

 rectly determined mean of a number of 

 vectors, such as X 2 and Y 2 . Hence such 

 means determined for the various dis- 

 tricts of the country have been desig- 

 nated 'normal storm tracks,' and are 

 shown for May in chart XVII. 



