504 



IUllKtin 84 



TABlfc: I. RECORDS OF LAST KILLINC. I'ROSTS IN SPRING AND FIRST KILLING 



FROSTS IN AUTUMN 



Station 



Length Average i Average First Last 



of j Elevation in \ in , in in 



record autumn i spring - autum i i spring 



Years 1 fcrt 



Prescott Drv-farni. 6 ' SCOS 



Holbrook 8 5069 



Prescott 8 . 5320 



St. John's 8 5650 



Snowflake 4 5600 



Flagstaff 11 6700 



Mesa 16 1244 



Tempe . 8 1165 



Phoenix Experiment 



Station 17 1108 



Phoenix 18 1108 



Peoria 10 1150 



Buckeye 16 980 



May 26 

 June 4 

 5 

 May 25 

 June 18 

 " 16 



Dec. 1 , Feb. 2? Oct. 21 Apr. 2 

 Nov. 24 j " 26 " 23 Mar. 3 



Dec. 6 ! " 16 Nov. 9 " 31 



Nov. 27 ' Mar. 8 : Oct. 22 | Apr. 19 



Dec. 14 ' Feb. 24 i Nov. 9 ' Mar. 25 



Nov. 23 Mar. 6 Oct. 22 Apr. 6 



ATMOSPHERIC MOVEMENTS 



As a whole, Arizona has low wind movements, but in certain 

 localities the topography is responsible for a number of windy days, 

 especially in spring. The Little Colorado drainage area, a funnel- 

 shaped basin 200 miles long and 150 miles wide at the lower end, 

 backed at the source by the White Mountains, and having a gentle 

 slope from side to side, is subject to high atmospheric movements 

 in certain seasons. 



In localized areas topographic features make probable frequent 

 recurrence of destructive blast winds. Two high winds, one ac- 

 cording to reports a tornado, passed over a portion of Anderson 

 mesa and the upper Willow Valley, the paths being about fifteen 

 miles apart. Three slightly destructive blast winds have occurred 

 at Tucson in as many years, but there are no reasons to svippose 

 that a well defined tornado path exists in any part of the State. 



The Sulphur Spring Valley, heading at the base of Graham 

 Mountain, terminates at a much lower elevation some one hundred 

 miles south in Mexico, and has topographic features favorable to 

 considerable atmospheric movements. A low range of hills cross- 

 ing the Valley near Pearce checks the lower currents somewhat ; 

 but, in general, the entire region may be characterized as having 

 fairly high wind movements, especially in spring. 



In southwestern Arizona the low hot areas which are adjacent 

 to cooler elevated regions are subject to sudden and rapid wind 



