l^ocOling Jfunb 



iy47_1948 Rl-:rORT OX Till': 27.0074-l)AV CYCLE IN 

 WASHINGTON PRECIPITATION 



By C. G. abbot 

 Research ^^ssociale, Sinilhsofiion Institution 



In Smithsonian Miscellaneous Collections ' I have set forth an ap- 

 parent cycle of precipitation at Washington, and the outcome from 

 year to year of yearly predictions based thereon. In 1947, for the 

 fourteenth consecutive year, the average precipitation for the predicted 

 favorable days has exceeded the average precipitation on all other days 

 of the year. The results for 1947 precipitation arc given in table i. 



Table i. — Statistics of Washington (irccipitation, i<^{7 



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



referred" days .. 0.171 0.100 0.030 0.128 0.136 0.284 0.084 0.035 0.150 0.000 0.216 0.058 0.1166 



her days 0.072 0.023 0.048 o.ioi 0.126 0.112 0.245 0.220 0.097 0.076 0.123 0.037 0.1058 



tio 2.38 4.29 0.62 1.22 1.08 2.54 0.34 0.16 1.5s 0.00 1.75 'S" '-'o 



tal inches 3.7a 1.65 1.24 3-37 405 S/6 S-3S 3-68 3.70 1.31 S09 147 40.39 



irni.il inches 3-S.S 3-27 3-7S 327 3-70 4.'3 47' 40i 3.24 2.84 2.37 3.32 42.16 



rcent normal .. 105 50 33 '03 '09 »39 ii4 92 114 46 215 44 96 



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

 "jireferred" and all other days. Line 3 gives the ratio: • 



Lines 4 and 5 give the total precipitation and normal precipitation in 

 inches, and line 6 the percentage of observed to normal for the UKMiths 

 and year. 



"Preferred" days iiad a higher average precipitation than all other 

 days in the months January, February, April, May, June, September, 

 November, and December, and also for the year 1947 as a whole. 

 Other days had a higher average precipitation than "preferred" days 

 in the months March, July, August, and October. Of these four e.x- 

 ccinional months, March and October had very low rainfall. The 

 average ratio, "perferred"/all other, of precipitation per day for 14 

 consecutive years has exceeded unity. The expectation is 1.42. The 

 value for 1947 is i.io, and for the 14 years it is 1.47. 



The following table 2 gives the dates for 1948 when the average 

 daily precipitation is expected to exceed the average for all other days. 

 In tiie first column are given in Roman numerals the day numbers 



'See Smithsonian Misc. Coll., vol. 104, No.s. 3 and 5, i<;44; -tkI vol. 107, 

 No. 3. I947- 



SMITHSONIAN MISCELLANfcOUS COLLECTIONS, VOL. 110, NO. 4 



I 



