374 
1958; Wilk, 1959]. In these networks, however, 
observers are often spaced so widely that exact 
definition of the areal extent of hail is impos- 
sible. Thus, crop-loss records are the best avail- 
able data for defining the extent of hailstorms in 
heavily insured areas. 
Hailstorm movement—The movement of each 
hailstorm was determined by examination of 
radar echoes at the time and location of hail 
occurrence. The direction of movement showed 
a seasonal change. In May and October, hail- 
storms moved from directions south of west. In 
July and August the preferred direction of 
movement shifted to the northwest quadrant. 
The direction of movement of hailstorms 
varies greatly seasonally and annually. Figure 
4 shows the percent of hailstorms moving from 
various directions each year, 1952 to 1957 in- 
clusive, and also shows the percent of the total 
damage each year which occurred with storms 
moving from the indicated direction. The most 
damaging storm in a given year may cause a 
high percentage of the total damage. The per- 
cent of the year’s damage caused by the major 
storm during each of the six years is indicated 
beside the damage bar of the direction from 
which the major storm moved. For example, in 
! 
1953 [ 
31 HAILSTORM DAYS 
3.09% OF TOTAL CROP DESTROYED 
10 
3 
PERCENT OF LIABILITY EXPOSED TO STORM 
a 
xo) 
5 10 15 20 25 30 35 
PERCENT OF EXPOSED CROP DESTROYED 
STOUT, BLACKMER, AND WILK 
1953 ten per cent of the storms moved from 
the west-northwest, causing 44% of the year’s 
damage. Most of this damage was caused by 
the storm of August 7, 1953, which produced 
43% of the year’s damage. 
Hailstorm intensity—Variations in hailstorm 
intensity may be studied using the percent of 
crop destroyed. This may be done by year, 
month, day, or hour for the heavily insured 
areas of the state. In this study, individual hail- 
storm days have been classified according to 
the areal extent of the storm and the intensity 
of the storm. The areal extent is given by the 
percent of the total insured crop in the state 
which was exposed to hail on a given day. The 
storm intensity is given by the percent of the 
exposed crop which was destroyed by hail. The 
distribution of storms in 1953 and 1957, clas- 
sified in this manner, is shown in Figure 5. The 
figure shows that storms had a tendency to be 
larger and more damaging in 1953 than in 1957. 
Local variations in intensity may be studied 
by plotting the percent of exposed crop in each 
section which was destroyed by hail. Maps 
showing intensity variations have been plotted 
for ten days with hail. Two of these maps are 
shown in Figures 6 and 7. 
10 
1957 
26 HAILSTORM DAYS 
0.22% OF TOTAL CROP DESTROYED 
PERCENT OF LIABILITY EXPOSED TO STORM 
‘ee-0-e—e 
a ees 
5 10 ihe} 20 25 30 35 
PERCENT OF EXPOSED CROP DESTROYED 
Fic. 5—Comparison of 1953 and 1957 storm area and intensity 
