not disposed to moisture. That the mountains to the north 

 and northwest of Los Angeles contributed to the deflection 

 of air currents upwards, tending to increase the convectional 

 currents, is proven by the fact that Monrovia, Glendora. and 

 other nearby towns reported heavier rainfall than either Pasa- 

 dena or Los xAngeles. 



To summarize: The cause of the heavy rain in Los An- 

 geles was generally the blocking: of aerial eddies westerly, 

 permitting the entrance of a southerly storm and specifically 

 the recurving of the path of the low area and the configuration 

 of the region about the San Gabriel River. 



-fc)' 



*The September Hot Wave. 



On September 17, 80 degrees was the highest minimum 

 temperature ever recorded in Los Angeles, and the highest 

 temperature. 108 degrees, on that day was within 1 degree of 

 the absolute maximum for the station, 109 degrees on July 25, 

 1891. That such conditions are uncommon may be gained 

 from the fact that this temperature was 26 degrees higher than 

 the mean daily maximum for the month from 37 years' record 

 at this station. Otherwise September was a typical month, 

 the mean highest temperature being only 2 degrees above the 

 daily normal maximum. 



The cause of this hot spell, like all instances of tempera- 

 tures above 90 degrees in this portion of Southern California, 

 was a well-defined "norther" condition brouc-ht about by pres- 

 sure distribution typical of such phenomena. 



On September 15 the barometric pressure was high over 

 the northwest and low in the southwest. While the low 

 area remained stationary for many davs, the high area pro- 

 gressed in a southeasterly direction. The greatest difference 

 in pressure was coincident with the warmest day, when the 

 weather map showed a gradient of a tenth of an inch in baro- 

 metric pressure to the hundred miles on an east and west line. 



The effect of this pressure distribution on the weather in 

 the coast districts of Southern California was to give that 

 region the driest and warmest day on record. Previous rec- 

 ords were broken at surrounding stations, notably that of San 

 Diec^o, which has the longest unbroken series of observations 

 in this section. At that station the thermometer rose 9 degrees 

 higher than ever before recorded, and 33 degrees above the 

 mean daily maximum temperature of the month. 



* "Monthly Weather Review." 1913. Vol. XLI. Pp. 1470-1471. 



