58 Gen. xi. W.Grcely — Rainfall Types of the United States. 



characteristics are scarcit}'' of precipitation during the spring 

 months, April being very decidedly the month of least rainfall 

 followed by October, and a heavy rainfall during the late sum- 

 mer and late autumn months with the maximum precipitation 

 in November and nearly as heavy rain in July or August. The 

 heavy I'ainfalls of the Saint Lawrence valley during November 

 are the more remarkable in view of the fact that in this month 

 the minimum precipitation occurs from northern Florida to 

 central New York. 



Detailed data regarding this type is not at hand, but Professor 

 Charles Carpmael, chief of the meteorological service of the 

 Dominion of Canada, is authority for the statement that the 

 minimum precipitation occurs in April at Kingston, Rockliffe, 

 Montreal, Quebec, Father point, Saugeen, and Parry sound, as 

 well as throughout the province of New Brunswick. It is in- 

 teresting to note that in the composite rainfall types of New- 

 foundland and New Brunswick, as well as along the greater 

 part of the Massachusetts and Maine coasts, the November max- 

 imum obtains, and is as a rule the principal maximum, with 

 March as the month of secondary maximum, although in some 

 localities these maxima are reversed in order of importance. 



There may possibly be added a Gulf type, so called from its 

 prevalence along the northern shores of the gulf of Mexico, 

 where the maximum rain falls in September and the minimum 

 in the early spring. Western Florida and the Texas coasts are 

 the only sections in which this obtains. The normal daily rain- 

 fall at Key West, Florida, of 47 years, is .107 inch, with depart- 

 ures as follows: January, — .038; February, — .050; March, 



— .062 ; April, — .064 ; May, — .006 ; June, .044 ; July, .022 ; 

 August, .055; September, .111; October, .053; November, 



— .038, and December, — .043 inch. 



It is not within the scope of this paper to discuss the special 

 causes which produce these differing types of rainfall distribu- 

 tion in North America. It may be said, however, that there is 

 no doubt in my mind that the maxima and minima phases of 

 precipitation are simply the result of the fluctuation throughout 

 the year of atmospheric pressure over North America and its 

 contiguous waters, thus affecting the relative positions of high 

 and low areas and consequently causing winds, either favorable 

 or unfavorable to precipitation, according to season and locality. 



