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1946-1947 REPORT ON THE 27.0074-DAY CYCLE IN 

 WASHINGTON PRECIPITATION 



By C. G. abbot 



Research Associate, Smithsouian Institution 



In Smithsonian Miscellaneous Collections volume 104, No. 21, I 

 reported on this cycle, and listed dates of 1946 when it was expected 

 that greater average precipitation would occur than on other dates. 



The following tabulation shows how the matter turned out. I give 

 average precipitation per day on "preferred" and other days. 



Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Year 



"PreferrcJ" .. 0.027 0.198 0.031 0.017 0.298 0.0023 0.186 0.169 0.156 0.168 0.074 0.025 0.113 



Other 0.060 0.018 0.076 0.113 0.132 0.139 0.0720.1030.107 0.008 0.0012 0.114 0.0777 



Ratio 0.45 II. o 0.41 0.15 2.26 0.016 2.58 1.64 1.46 21. 60. 0.22 1.45 



Total, inches .. 1.54 2.84 1.84 1.88 6.74 2.38 3.82 4.18 3.95 2.50 1.05 2.02 34.74 



Normal, inches. 3.55 3-27 3-76 3-27 3-70 4-13 -t-7i 4-oi 3.24 2.84 j.37 ,^.32 42.16 



Percent, norijial. 44 87 49 58 182 58 81 104 122 88 44 61 82 



"Preferred" days had higher average precipitation than utiier day.s 

 in the months of February, May, July, August, September, October, 

 and November. The contrary happened in January, March, April, 

 June, and December. Of these unfavorable months all were ex- 

 ceptionally dry. But November, also very dry, turned out favorably. 



For the complete year 1946, the ratio of average daily precipita- 

 tions, "preferred" to other days, is 1.45. It is the thirteenth con- 

 secutive year in which this ratio has exceeded unity. The mathemati- 

 cal expectation for its value is 1.42.^ The average ratio for 13 years 

 is 1.50. 



The following table gives the dates for 1947 when the average 

 daily precipitation is expected to exceed that for all other days. In 

 the first column are given in Roman numerals the date numbers 

 within the 2^/ days of the cycle when higher average precipitation 

 is expected. The remainder of the table gives the actual dates in the 

 different months which correspond to these Roman numerals. These 

 "preferred" dates should, on the average, give higher precipitation 

 than other dates. 



It should be emphasized that this prediction relates only to Wash- 

 ington, D. C. 



^ See my original paper, Smithsonian Misc. Coll., vol. 104, No. 3, 1044. Also 

 see vol. 104, No. 5, pp. 37-42, 1944. 



SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 107, NO. 3 



