80 CALIFORNIA ACADEMY OF SCIENCES. 



trates the superimposing of a series of daily charts showing 

 this feature. 



Indeed, if only the observations of a single station are 

 studied, taking a specific instance of the recurrence of a 

 persistent weather type, the list of days in which rain of 

 any consequence fell on successive days in San Francisco 

 during the last rainy season, shows six such periods lasting 

 from six to fifteen days each. These periods of the rainy 

 season, and the contrasting conditions of rain absence inter- 

 vening, are the special object of this inquiry. 



I now come to determining and naming these w^eather 

 types, commencing with the rainy season of 1885-6. On 

 November 1st, the first interruption of the dry season of 

 1885, disregarding some slight rains occurring prior to this 

 date, began at the time when the high, which had moved 

 inward from the coast with the advance of the season and 

 finally hung stationary over the eastern slope of the Cascade 

 Range, moved further eastward before the low area advanc- 

 ing on the Washington Territory coast from sea. This 

 low area spread south and brought the rainy season for San 

 Francisco and this portion of the State. This type I call 

 the 



NORTH PACIFIC CYCLONIC. 



It prevailed from November 1st to 10th, and from Janu- 

 ary 11th to 14th, and is distinguished by a low barometer 

 area of considerable depth over and to the westward of Or- 

 egon and Washington Territory, which, striking the mount- 

 ain range and high pressure to the eastward, cannot break 

 over the barrier, and is held there with fluctuating depth 

 for some time. 



The high, which always exists somewhere in the margin 

 of the low, continues central in the district north of Salt 

 Lake. During the prevalence of this type, southerly gales 

 occur from Cape Mendocino to Vancouver Island. Rain 

 prevails and frequently becomes heavy over Oregon, Wash- 

 ington Territory, in California south to San Luis Obispo 



