National Geographic : 1905 Jun
FORECASTING THE WI 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 X, 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 w------ ,Sa/e ofA/t/ mo o /oo .,,.: __ CHART XVI -Showing method followed in d normal storm tracks and in ascertaining th value to represent the pressure exerted on center that causes it to depart from a normal t 26, as follows : To the north, o. io inch; northeast, o oo; 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 Y, 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 FATHER AND STORMS 297 directions, as follows: To the north,o. 30 inch; northeast, o 20; east, 0.60; south east, 0.30; south, o. o ; southwest, o. o ; west, o.io, 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 S of which, X,, being the result S\ ant of the pressure exerted on the storm, the other, X,, will \ represent the 24-hourvaluethat ' should be given the general circulation of the atmosphere That carried the storm with it. S Similarly, Y, represents the 24 7! 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, representing the 24 hour values of the general cir culation on the two dates, are of equal length and vary not S more than 3 degrees 30 min 200 3 ° 0 utes in direction, from which it may be assumed that the general circulation of the at mosphere in May that carries developing the storms of the region of New e correct Mexico and northwest Texas a storm with it may be represented by rack. 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, and Y,. 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.