314 Twe;nty-se;ve;nth Annual Re;port 



frosts in central and southern Arizona are very uncommon, and when 

 they do occur it is during December and January. 



Referring to Weather Bureau reports for aU points within the 

 State, the mean annual temperatures for 1911, 1912, and 1913 were 

 the lowest for many years. The minimum temperatures for 1911 and 

 1912 were not unusual, but the January freeze of 1913 was the most 

 severe within the history of the State. ■ On January 6, 7, and 8 the 

 lowest temperatures ever known were recorded in nearly all sections. 

 The maximum temperature is usually reached during June or July. 

 May, 1910, was abnormally warm, breaking all previous records for 

 May, and the temperatures of May 29 or 30 are, in most instances, the 

 maximum temperatures reached during a period of many years. How- 

 ever, considering the high day-time temperatures of Arizona from a 

 human standpoint, it must be remembered that the thermometer is not 

 a reliable indicator of physical comfort. Heat is rapidly dissipated from 

 the body by reason of excessive evaporation due to the extreme dryness 

 of the atmosphere. This dryness, with almost constant breezes, renders 

 the temperatures, that in more humid sections would be intolerable, 

 easily endurable. The daily range in temperature is great, being from 

 30 to 60 degrees, and the resulting cooler nights during the hot season 

 are most enjoyable. 



There are two rainy seasons, the more distinct one beginning each 

 year early in July and ending about the middle of September. The rains 

 during this season are usually local and of short duration, but torrential 

 in character. The other rainy season is not so well defined, and pre- 

 cipitation may occur in the early winter, or as is more usually the case, 

 in February and March. Much of the precipitation at higher altitudes 

 in the winter months is in the form of snow. So much depends on the 

 timeliness of the rainfall that the total precipitation for the year is not a 

 certain indication of its effectiveness. Although the av^erage rainfall 

 for the State for 1913 was but slightly below the normal, the year was 

 exceptionally unfavorable for all interests dependent upon adequate and 

 timely precipitation. Bulletins 64, 65, and 70 of the Arizona Agricul- 

 tural Experiment Station contain excellent discussions of the character 

 and extent of the rainfall of Arizona with its bearino- on irrieation, 

 grazing and agriculture. 



Tables XXIX and XXX show some monthly and annual data for 

 the year 1916. 



The temperatures for the year for the State as a whole may be 

 considered as about normal. A frost March 25 and 26 badly damaged 



