34 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



14- 



la 



o 



fX 

 <4 



O 



■z 



1-2. 



z 

 tJJ 

 o 

 or 



m 



Fig. 27.— Exact length of the 273-month master period. 



even more months, evidently for the same features. If these shifts 

 could be predicted and corrected in advance, very high correlation 

 coefficients would exist between predictions and events. As it is, 

 correlation coefficients run from +50 to +70 percent at the dif- 

 ferent cities for precipitation, and from +30 to +50 percent for 

 temperature reckoned from absolute zero. 



9. ACCURACY OF PREDICTIONS 

 The average percentage difference between forecasts and events 

 runs from 15 to 30 percent for monthly precipitation values at dif- 

 ferent cities. It runs from 1.5° to 2.7° F. monthly for temperature 



