STOUT, BLACKMER, AND WILK 
CHAMPAIGN - URBANA 
Fie. 3—Location of hail on August 9, 1954 
Tasie 1—Areal extent of hailstorms 
Year 
Item : 
| 1952] 1953 | 1954 | 1955 | 1956 | 1957 
| “ 
Percent of crop loss dur- | 0.78) 3.09) 2.46) 0.43) 1.18) 0.22 
ing year 
Number of hailstorm |21 31 40 34 49 26 
days 
Percent of storm days | 81 94 75 74 65 69 
with swaths 
Average number of | 2 3 2 2 2 1 
swaths per storm day 
Average length of swath, |18.0 
mi 
Average width of swath, | 5.5 | 6.0 
mi 
Average spacing  be- pe 4) aki 20 20 28 
tween swaths, mi 
Average area of swaths, 
sq mi 
Average area of hail re- 
gion, sq mi 
31.5 
99 174 = |224 94 116 = |220 
18, 000) 20, 000)17 , 000/18, 000/15, 000 
Illinois in 1954. It was comparable in extent to 
the storm of August 7, 1953, since it also af- 
fected three per cent of the crops. 
All of the maps showing location of hail for 
the period 1952 to 1957, inclusive, were ex- 
amined and information tabulated concerning 
the number, length, and width of swaths. In 
addition, the rectangular area necessary to en- 
close all reports of hail on a storm day was 
computed. This area is called the hail region. 
Table 1 presents statistics relating to the areal 
extent of the storms in various years. 
The reason for the variations from year to 
year, as shown in Table 1, has not been in- 
vestigated but may be related to long-period 
variations in such atmospheric parameters as 
zonal wind speed, temperature, and moisture 
distribution. Detailed information of this type 
is necessary to define the extent of hail more 
accurately. Information on the extent of hail 
provides knowledge of the volume of the at- 
mosphere which is contributing to the forma- 
tion of the hail. The need for more detailed 
data on hail occurrence for use in evaluating 
radar for identification of hailstorms has led to 
the establishment of hail observer networks 
[Donaldson, 1958; Douglas and Hitschfeld, 
