-i vi'K AGRIC1 in KAI. SOCIETY. 40'. > 



v 



[ndeed, if only the observations of a single station arc studied, taking a 



specific instance o( the recurrence of a persistent weather type, the list of 

 days in which rain of any consequence fell on successive days in San Fran- 

 cisco during the last rainy season (1885-86), shows six such periods, last- 

 ing from six to fifteen days each. These periods of the rainy season, and 

 the contrasting conditions of rain absence intervening, arc the special object 

 of this inquiry. 



1 now come to determining and naming these weather types, commenc- 

 ing with the rainy season of 1885-86. On November first , the first inter- 

 ruption 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 sta- 

 tionary over the eastern slope of the Cascade Range, moved further east- 

 ward before the low area advancing 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 first to tenth, and from January eleventh to 

 fourteenth, and is distinguished by a low barometer area of considerable 

 depth over and to the westward of Oregon and Washington Territory; 

 which, striking the mountain range and high pressure to the eastward, can- 

 not 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, con- 

 tinues 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, Washington Ter- 

 ritory, in California south to San Luis Obispo, and in the San Joaquin 

 Valley. 



The temperature throughout the coast is about normal. It is only when 

 a subsidiary low is developed in southeastern California, locally called a 

 " Sonora storm," that rain spreads over the southern part of the State, 

 being generally of short duration. See Plate III as an example of the 

 conditions existing during this type. 



Interior Anti-Cyclonic Type. 



This second type closely resembles the preceding in that the interior high 

 is well marked, but differs in that the low upon the coast is less in depth. 

 This type prevailed from November eleventh to fifteenth; November 

 twenty-fifth to December sixth; December fourteenth to twenty-sixth; 

 January twenty-seventh to February twelfth. It is characterized by a 

 high barometer (about 30.30 inches) over Utah, Nevada, and Southern 

 Idaho. The accompanying low barometer on the northern coast drops 

 down frequently to 29.70°, and is central west of Washington Territory. 

 These lows appear to beat against the high, the low area often dropping 

 down for a short time nearly to Cape Mendocino. At other times they 

 push the high southerly over Arizona, and pass eastward beyond our 

 boundary. Again, when the surge of high pressure is very great oyer 

 Idaho, a low often pushes upon it from the southwest coast of California, 

 at which time rain may occur in light showers on the southern coast. 

 The rainfall, except as just mentioned, never passes south of San Fran- 

 cisco, and is generally limited to light showers in Oregon and Washington 



