Table 4 . - -Average depth of preoip-Ltat-iorij in inches 3 and average number of storms by 

 month and precipitation zone 







June 



: July 



: Aug 



ust : September 







Average 









No. of 





No. of 





No. of: : 



No. 



of: 







No. of 



Zone : 



Depth : 



S UOTIUS 



: Depth: 



storms 



: Depth: 



storms : Depth : 



storms : 



Depth : 



s torms 











DAVIS COUNTY EXPERIMENTAL WATERSHED 













1 



1 



36 



7 . 3 



.34 



2.0 



1.07 



4.7 .76 



4 



. 4 





.88 



4.6 



2 



1 



94 



5.5 



.63 



2.4 



1.21 



4.1 1.28 



4 



.0 



1 



.26 



4.0 



3 



1 



19 



4.7 



.50 



3.1 



1.15 



4.8 1.04 



4 



.9 





.97 



4.4 



4 



1 



35 



5.4 



.61 



3.6 



1.10 



4.9 .92 



4 



.6 



1 



.00 



4.6 



Average 



1 



46 



5.7 



.52 



2.8 



1.13 



4.6 1.00 



4 



.5 



1 



.03 



4.4 











GREAT 



BASIN 



EXPERIMENTAL AREA 













1 







60 



1.1 



0.59 



6.4 



0.73 



8.6 0.79 



6 



.4 







.68 



7.3 



2 



1 



53 



11 .3 



1.01 



8.2 



1.15 



9.3 .93 



7 



.3 



1 



.16 



9.0 



3 



1 



30 



9.4 



1.41 



11.4 



1.62 



13.2 1.38 



10 



. 3 



1 



.43 



11.1 



4 



2 



47 



11.0 



1.41 



10.4 



1.48 



12.3 .98 



8 



.0 



1 



.58 



10.4 



Average 



1 



48 



9.8 



1.10 



9.1 



1.24 



10.8 1.02 



8 



.0 



1 



.21 



9.4 



Storm Occurrence by Hour 



On the average, the Great Basin area receives more than twice as many storms during 

 the period June- Sept ember than does the Davis County area (table 4). 



Between the two areas, differences in hour of storm occurrence are much more 

 striking than are zonal differences (figures 5, 6). The inset in each of figures 5 

 and 6 is a schematic showing the distribution of storms by hour; in each, midnight is 

 adjusted to zero. The insets cannot be used to derive figures 5 or 6. 



The curve for the Great Basin area is of the S-type, while that for the Davis County 

 area is more linear- -slightly concave upward. Thus, only 13 percent of the storms in 

 the Great Basin area occur before 0600 hours, 45 percent before 1200 hours, and 84 per- 

 cent before 1800 hours. On the Davis County area, 22 percent occur before 0600 hours, 

 45 percent before 1200 hours, and 72 percent before 1800 hours. In general, the pattern 

 of storm occurrence in the Great Basin area conforms to the popular concept that most 

 of the storms occur between 1000 and 1800 hours, peaking at about 1300 hours. However, 

 the pattern in the Davis County area does not; it is more nearly uniform. There is a 

 slight but steady increase in storm occurrence up until 2000 hours followed by a sharp 

 decrease up until midnight. These differences in storm occurrence are probably associ- 

 ated with the principal source of summer moisture and atmospheric instability mechanisms. 

 In the Great Basin area, thermal convection is the principal source of thunderstorms and 

 the Gulf of Mexico is the chief source of moisture. In the Davis County area, two 



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