EFFECTS OF FREEZES ON CITRUS IN CALIFORNIA 251 



In general throughout the citrus belt the Sunday night cold was 

 accompanied by a strong wind that blew throughout the night. By 

 Monday night, January 6, the wind had died down, but the cold was 

 unabated; and on Monday night and Tuesday morning the tempera- 

 ture went lower than it had gone the night before. Tuesday night 

 and Wednesday morning were also cold, sufficiently so in most of the 

 citrus districts to freeze fruit. After this, the temperature became 

 more moderate, although for several days the skies were cloudy and 

 the weather stayed cool. On the 9th and 10th, there were light rains 

 in most sections and heavier rains about the middle of the month. 

 The month of January as a whole was the coldest January for fifteen 

 years; while the cold spell from the 5th to the 8th was the coldest 

 weather ever experienced by citrus growers in southern California. 



Heretofore cold spells have usually, occurred on still, cloudless 

 nights. On such nights the air becomes stratified, the colder strata 

 resting on the ground. A breeze improves the temperatures at such 

 times by mixing the strata of warm air with those of colder air. The 

 freeze of 1913, however, was very different from previous periods of 

 cold. It was preceded by strong winds which came from the north- 

 west and north. Mr. A. G. McAdie, of the United States Weather 

 Bureau, has called attention to the fact that the winds preceding 

 frosts in California usually come from the northeast. He points out 

 that this year the cold wind came from the north and northwest, 

 moving directly over the Sierra Madre Mountains, with their elevation 

 of six thousand feet, instead of taking the customary course through 

 the El Cajon Pass. 



The temperature records reported from various places are in gen- 

 eral so inaccurate that little dependence can be placed upon them. 

 The Weather Bureau records are thus the best ones that can be 

 taken for comparison. True, these records do not represent grove 

 records, but they are at least comparative for different places. The 

 following table supplied by Dr. Ford A. Carpenter, in charge of the 

 Los Angeles Observatory, U. S. Department of Agriculture, Weather 

 Bureau, gives the maximum and minimum records for the period of 

 the freeze for various points in California. 



The minimum temperatures reported from the different parts of 

 southern California show a range from 25 F. to 2 F. The accu- 

 racy of these extremes may well be questioned. It may safely be 

 concluded that most citrus districts reached a temperature as low as 

 18 F. Several places have reliable records as low as 15 F., and a 

 few places show apparently reliable records as low as 12 F. In many 

 sections the temperature remained at or below freezing for sixty 

 hours. 



