WEATHER TYPES ON THE PACIFIC COAST. 77 



WEATHER TYPES ON THE PACIFIC COAST. 



By W, A. Glassford, 2d Lient. Signal Corps, U. S. A. Assistant. 

 (With Four Plates.) 



A short study of the charted weather reports of the Pa- 

 cific Coast, reveals certain types lasting for a considerable 

 period which admit of classification. East of the Rocky 

 Mountains, however, no such characteristics are present; 

 the storms or cyclonic areas, as well as the anti-cyclonic or 

 areas of high pressure generally originate in the Gulf of 

 Mexico, the Eocky Mountain slopes, or in British America, 

 and move in succession over a curved path almost invariably 

 to the eastward at a uniform rate, and with uniform charac- 

 teristics. They disappear as regularly near Nova Scotia. 

 It is very seldom, if ever, that perfect paths of low pressure 

 areas are traced from the Pacific Coast across the mountain 

 plateaus and ranges, although some few cases have been 

 charted on the storm track maps; but even these are not so 

 uniform as in the East, for they frequently tarry for quite 

 a period, clinging to some valley or plateau. On this coast 

 a noticeable feature is the difference in the storm frequency 

 between the northern and southern boundary lines of the 

 United States. Areas of low pressure of any intensity are 

 of infrequent occurrence in southern California, but going 

 north become more frequent as Vancouver Island is ap- 

 proached. From a search of the Weather Eeviews for three 

 years, it is found that areas of low pressure entering the 

 Pacific Coast states from the ocean during that period num- 

 ber 90; those north of the 45th parallel are 54; between 45^^ 

 and 40°, 25; between 40° and 35°, 10; below the 35th par- 

 allel, 1. Another peculiarity of the areas of high and low 

 pressure here is their arrangement in recurring and symmet- 

 rical types; recurring, because there is a tendency to assume 

 the same barometric condition on successive days; symmet- 



7— Bull. Cal. Acad. Sci. H. 5. Issued Aug. 31, 1886. 



