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A LONG-RANGE FORECAST OF UNITED STATES 

 PRECIPITATION 



By C. G. Abbot 

 Research Associate, Smithsonian Institution 



FOREWORD 



A hidden family of harmonic regular periods exists in weather. 

 The periodic members of this family persist with unchanged lengths 

 for scores of years. By determining their average forms and ampli- 

 tudes for intervals of a thousand months, successful forecasts may 

 be made for years to come; or backcasts may be made for former 

 years and compared to former events. Agreement of such backcasts 

 with the records warrants confidence in future forecasts. 



These claims seem preposterous to most meteorologists. Therefore, 

 before proceeding to explain the method and to give forecasts to 1967 

 for 32 cities of the United States, illustrative forecasts for the years 

 1950 to 1958 will now be shown and compared to the records of that 

 interval graphically. 



Figures 1, 2, and 3 show forecasts (dotted) and the observed march 

 of precipitation, 1950-1958. These curves represent 3-month running 

 means, and are expressed in percentages of normal precipitation. Fig- 

 ure 1 represents precipitation at Madison, Wis., and figure 2 at Nash- 

 ville, Tenn. The curve at the top of figure 2 will be described later. 

 Figure 3 shows forecast and observation for Sacramento, Calif. 



I have computed for several cities coefficients of correlation be- 

 tween my forecasts and the observed precipitation for the years 1950 

 through 1958. They are as follows : Washington, D. C, 52.3 percent ; 

 Cincinnati, Ohio, 57.3 percent ; Nashville, Tenn., 59.0 percent ; Inde- 

 pendence, Kans., 52.0 percent ; Madison, Wis., 56.6 percent ; Sacra- 

 mento, Calif., 69.0 percent. 



These coefficients indicate that my forecasts are over halfway to- 

 ward perfect long-range prediction of weather. There still remain 

 undisclosed variables that produce the discrepancy of about 40 percent 

 between my coefficients and perfect correlation. 



SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 139, NO. 9 



