1948-1949 REPORT ON THE 27.0074-DAY CYCLE IN 

 WASHINGTON PRECIPITATION 



By C. G. abbot 



Research Associate, Smithsonian Institution 



In Smithsonian Miscellaneous Collections^ I have set forth an 

 apparent cycle of precipitation at Washington associated with the 

 sun's rotation. In 1948, for the fifteenth consecutive year, the aver- 

 age precipitation for predicted favorable days has exceeded the aver- 

 age precipitation on all other days of the year. The results for 1948 

 precipitation are given in table i. 



Table i.— Statistics of Washington precipitation, 1948 



Jan. Feb. Mar. Apr. May Ji 



Average f Pfd. .. 0.292 0.049 0.274 0.146 0.386 o 



per day \ Other . 0.038 0.091 0.087 0.007 0.161 o 



Ratio 7.68 0.54 3-15 20.8 2.40 o 



Total ppt 4.99 2.05 5. 31 2.44 8.59 3 



Normal 3-5S 3-37 3-75 3-27 3-70 4 



Percent 141 61 142 75 232 



Lines i and 2 give the average precipitation in inches per day for 

 preferred and all other days of the year 1948. Line 3 gives the ratio : 



preferred Lines 4 and 5 give the total precipitation and normal 

 other 

 precipitation in inches, and line 6 gives the percentage of normal pre- 

 cipitation falling in the several months, and in the entire year. 



Preferred days had a higher average precipitation than other days 

 in the 5 months January, March, April, May, and December, and 

 in the year as a whole. The other 7 months went the other way, but 

 November had almost an exact balance between preferred and other 

 days. However, if on June 19, August i, September 21, October 5, 

 and November 28 precipitation had been delayed a few hours and 

 occurred on the next following days, these 5 months would also have 

 been favorable to the preferred days. 



Statistically, the ratio: "preferred'' j^ expected to be 1.42. The 

 other 

 ratio for the 15 years ending with 1948 has actually been 1.46. 



Table 2 gives the dates for 1949 when the average daily precipi- 

 tation is expected to exceed the average daily precipitation on all 

 other days of the year. In the first column are given in Roman 

 numerals the day number of the 27 days of the cycle when higher 

 precipitation is expected. The remainder of the table gives the 

 actual dates in the different months which correspond to these Roman 



1 Smithsonian Alisc. Coll., vol. 104, Nos. 3 and 5, 1944! vol. no, No. 4, 1948. 



SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. Ill, NO. 5 



