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MILES 
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Fie. 1—Annual average hail distribution ex- 
pressed as number of days with hail per ten-year 
period 
is a part of a non-orographic hail belt extending 
from Oklahoma to Pennsylvania, coincides 
roughly with a region of strong frontal activity. 
Summer hail distribution—The average fre- 
quency distribution of hail days durimg the 
three summer months of June, July, and August 
is similar to the annual hail frequency shown in 
Figure 1. However, the maximum in extreme 
southern Illinois is not present. Furthermore, 
the area of highest hail frequency is located in 
northwestern Illinois rather than in the area 
west of Springfield. The annual hail minimum 
west of Peoria appears pronounced in the sum- 
mer. 
Months of maximum hail occurrence—In 
general, the month of maximum hail activity is 
March, April, or May in the southern portion 
and April, May, or June in the northern half. 
Eight days with hail are average for May, six 
days for April, and between five and six days 
per month for March and June. The frequency 
STOUT, BLACKMER, AND WILK 
of hail days declines through the summer and 
fall seasons, with an average of four hail days 
in July, three in August, and between one and 
two in September and October. 
Reliability of distribution patterns—Since 
there was some question whether the hail maxima 
in northwestern, southwest central, and southern 
Illinois were persistent or had been induced by a 
few years of unusually heavy hail oceurrence in 
these areas, the reliability of the hail distribution 
pattern was investigated. Hail maps for each of 
the five decades in the 1901-50 period were 
drawn. It was found the three maxima areas per- 
sisted throughout this 50-year period, although 
some deviations from the pattern of Figure 1 
were apparent im the various decades. In general, 
the five ten-year periods showed patterns similar 
to the average pattern of Figure 1 with respect 
to outstanding features. However, some major 
pattern differences did appear from decade to 
decade. 
To illustrate time variability further in the 
number and distribution of hailstorms in the 
State, hail occurrence maps for separate years 
were prepared. It was found, for example, that 
a relatively large number of hailstorms oceurred 
over a large portion of the State during 1911. 
Individual station amounts ranged from zero 
to nine. In contrast, in 1935 hail was relatively 
sparse. The maximum number of storms re- 
corded at any station was four, and the majority 
of the stations had none or only one storm. In 
1936, again relatively few hailstorms occurred 
with a maximum number of four in northwestern 
Illinois and large areas of zero or one over the 
rest of the state. 
Analysis of crop-hail loss data—Variations 
in the hail hazard in Illinois are being studied 
using records of paid hail losses compiled by the 
Crop-Hail Insurance Actuarial Association 
(CHIAA) [Roth, 1955]. The purpose of the 
study is to determine whether or not meteoro- 
logical parameters can be used to define varia- 
tions in the hail hazard, and, consequently, be 
employed in establishing hail insurance rates for 
various areas. 
The records of paid hail losses include the 
year, month, day, and hour of hail occurrence; 
the county, township, and section (square mile) 
where hail occurred; the rate or percent of loss 
caused by the hail; and the type of crop dam- 
aged. In addition to the hail loss records for 
the period 1952-57, radar data of the Illinois 
