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PERIODIC INFLUENCES ON WASHINGTON 



AND NEW YORK WEATHER OF 



1949 AND 1950 



By C. G. abbot 



Research Associate, Smithsonian Institution 



A. PRECIPITATION AT WASHINGTON 



In Smithsonian Miscellaneous Collections,^ I have traced the in- 

 fluence of a cycle of 27.0074 days on Washington precipitation. This 

 cycle is thought to be associated with the rotation period of the sun. 

 Dates were assigned when it was expected that, on the whole, greater 

 average precipitation would fall in Washington than on the average 

 of all other dates. In 1949, for the sixteenth consecutive year, this 

 proved to be so. The ratio of average daily precipitation on pre- 

 ferred dates of 1949 to average daily precipitation on all other dates 

 was 1.56. Basic statistical study of the years 1924 to 1941, inclusive, 

 indicated the expected ratio to be 1.42. The average ratio for 16 

 years ending with 1949 is 1.47. In detail the year 1949 yielded the 

 following values : 



Table i. — Statistics of Washington precipitation, 1949 

 (Values in inches) 



Average ) Pfd. . . . 

 per day ) All other 

 . Pfd. 



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

 219 0.143 0.207 0.098 0.229 0.044 0.070 0.269 0.209 0.024 0.02s 0.067 0.137 

 090 0.053 0.040 0.139 0.077 0.220 0.000 0.039 0.0161 0.025 0.043 0.088 



3.90 2.4s 1. 6s 0.57 0.32 * 5.40 o.is 1. 00 1.5- i.s6 



3.96 2.01 S-6s 1.85 4-57 4-57 3-5S 3-2i 0.74 i-7^ 40.12 

 3-75 3-27 3-70 4-13 4-7i 4-oi 3-24 2.84 2.37 3.32 42.46 



Other 



''Total ppt S 



Normal ppt 3 __ 



Percent of normal . . 143 98 106 61 153 45 97 ii4 no 113 31 



Infinitely large. 



Preferred days of 1949 had a higher average precipitation than 

 all other days in all months but June, July, and October.- 



1 Smithsonian Misc. Coll., vol. 104, Nos. 3 and 5, 1944; vol. no, No. 4. 1948: 

 vol. Ill, No. 5, 1949. 



2 In November recorded rainfall averaged the same in both groups, but traces 

 of rain fell on 4 preferred days and on only 3 other days. During July and 

 August rain fell copiously in northern Washington, and nearby, on preferred 

 days when none was recorded at the Weather Bureau. 



SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. Ill, NO. 17 



