408 TRANSACTIONS OF THE 



Another observation may be noted. When severe and stormy weather 

 prevails on this coast, and especially in California, almost invariably the 

 press dispatches announce from the East the prevalence of cold waves, snow 

 blockades, tornadoes, etc. If complaint be made at any time that the climate 

 of the Pacific Coast is in no way superior to the ordinary eastern weather, 

 attention may be drawn to the fact that at that time cold waves, snows, 

 etc., prevail over the East; if here the winds are high, they are balanced 

 by tornadoes or hurricanes there; if washouts delay travel on this slope, 

 floods in the streams of the great eastern valleys and seaboard do vastly 

 more damage; if frost nip the buds in our California citrus belt, in Florida 

 oranges are frozen. Such is the action of storms on this coast relative to 

 the margin of the great arctic high pressure ridges which surge down from 

 British Columbia. These coincidences show a common sensitiveness to 

 distant weather conditions. Contrary to the usual rule in the States east 

 of the Rocky Mountains, we have observed here a recurrence and persist- 

 ence of fine 'clear weather, or of rainy days for quite a period. The 

 interruptions are slight, of short duration, and the prevalent types are 

 unmistakable. The synoptic charts during these periods show a general 

 resemblance. For instance, during February last scarcely any rain fell. 



In April we had almost constant rain from the first to the seventeenth, 

 then followed suddenly, clear weather to the month's end and after. The 

 fact that the change from one type to another is so very sudden, is what 

 causes the difficulty on this coast in forecasting the weather. These phe- 

 nomena, as aids to forecasting, I call weather types. 



This study is only possible by reference to the reports of the observations 

 taken three times a day simultaneously at 4 a. m., noon, and 7 p. m., Pacific 

 time, telegraphed to San Francisco, and charted by entry on outline maps. 

 Isobars and isotherms are drawn, showing the belts or areas of like pres- 

 sure and temperature, and symbols are added marking stations where rain 

 has fallen or cloudiness exists. It is seen that map after map, day after 

 day, is almost identical. A persistence of some one barometric character- 

 istic covers the same region. Applying the principle of composite photog- 

 raphy, taking a transparent outline map of the same scale as the weather 

 map and drawing lines inclosing like areas, and continuing this process 

 on the same transparent map, we have represented a great number of like 

 areas superimposed upon each other. 



We thus find the high or low barometer regions to correspond with cer- 

 tain characteristic conditions of cloudiness and rain, which remain station- 

 ary and hover over the same locality during the continuance of the high or 

 low. For instance, grouping all the charts that have high pressure over 

 Oregon, and the low over southeastern California, it is noticed that remark- 

 ably fine warm weather, with northwesterly winds, continues for. a succes- 

 sion of days, while this condition lasts. When the barometer changes, it 

 does so suddenly, and the weather changes with equal rapidity. The 

 greater the number of these like features of barometer and weather found, 

 the greater, of course, is the frequency of the type. Illustrating in the case 

 of February last, it is found that a persistent high overlay the district 

 embracing Oregon, with parts of Nevada and Idaho. Plate II illustrates 

 the superimposing of a series of daily charts showing this feature.* 



* Note. — The plates show in figures for each station : First, temperature ; second, barom- 

 eter; third, wind velocity, and (when reported) the maximum velocity since the last 

 report, in brackets; fourth, the amount of rainfall. The wind direction is shown by an 

 arrow flying with the wind. The state of the weather at the time of the report is shown 

 thus: Cloudy or fair day, circles are fully or one half shaded; rain, by L. 11. or H. II., as it 

 is heavy or light; S., for snow. 



