CLIMATIC CONDITIONS OF THE UNITED STATES. 269 



A includes April 1 to 5, group B April 2 to 6, group C April 3 to 7, etc., 

 it follows that the period April 1 to 8 (inclusive) is a ''rainy" one; 

 the period April 9 to 10 is "dry"; that of April 11 (a single day) is 

 "rainy"; that of April 12 to 13 is "dry," etc. 



The dates of beginning and ending of each normally "rainy" and 

 normally "dry" period of the normal frostless season having been thus 

 obtained for each station, the length of each period is noted, in days, 

 and the lengths of the longest normally rainy period and of the longest 

 normally dry period become the two indices desired for the station in 

 question. 



The beginning and ending and the length of each normally dry 

 period in the period of the average frostless season are given in the 

 second column of table 14, and the corresponding dates and length of 

 the longest normally rainy period are given in the third column. Roman 

 numerals refer to months, the arable numerals not in parentheses 

 represent the days of the month, and these data are followed, in each 

 case, by the length of the period, in parentheses. Thus, the longest 

 normally rainy period in the period of the average frostless season for 

 Anniston, Alabama, extends from May 18 to September 8 and includes 

 114 days. 



As has been remarked, this method of treatment is quite arbitrary, 

 but it seems to furnish indices of normal raininess and droughtiness 

 that may be valuable. At least, these indices are worthy of a test, 

 and may be employed till more satisfactory ones may be devised. It 

 should be noted that the smoothing process applied to the precipita- 

 tion data by Bigelow (in deriving the daily normals) is here overlaid 

 by another very efficient smoothing process of our own (the use of 5-day 

 averages), so that the natural irregularity of precipitation is very 

 largely obUterated, which is to be desired when normals are requisite. 

 It may also be mentioned that the indices here set forth might have a 

 still greater value for such work as this if the constant 0.10 inch were 

 made somewhat smaller. Such an alteration would of course render 

 the normally rainy periods longer and the normally dry periods 

 shorter. The testing of such modifications may, however, be left to a 

 later time, and to other workers, if they will take up this important 

 phase of the climatology of precipitation. 



