Hail Studies in Hlinois Relating to Cloud Physics 
G. E. Srour, R. H. Buackmerr, anp K. E. Wik 
Illinois State Water Survey Division, Urbana, Illinois 
Abstract—Three independent hail studies during the past year have provided con- 
siderable basic knowledge concerning Illinois hailstorms. Analysis of climatological 
records from 85 stations indicates marked spatial and seasonal differences in frequency 
of hailstorms within the State. Considerable variability also occurs from year to year 
and decade to decade. 
One hundred eighty days with hail which caused damage to crops during 1953-1957 
have been studied using insurance records or crop-loss, radar, and synoptic data. The 
crop-loss data were plotted to determine the time, location, and areal extent of the 
hailstorms. Variations in hail intensity (per cent of crop damage) were also examined. 
Detailed case studies of the most significant hailstorms were made using radar and 
severe local storm volunteer observer data. It was found that distortions in squall lines 
corresponded closely with areas of greatest hail and wind occurrence. A case of hail 
formation in advance of a squall line was examined. Radar and rawinsonde data were 
used to formulate an hypothesis of the advanced hail formation process. 
Introduction—Three studies of hail are cur- 
rently in progress at the Illmois State Water 
Survey. The first study involves the use of the 
records of the U. 8. Weather Bureau coopera- 
tive substations and first-order stations. These 
records provide data on the frequency of hail- 
storms throughout Illinois. The data are studied 
to determine if the climatological differences 
can be related to physical processes involving 
the formation and dissipation of hailstorms. 
The second of these studies, supported by the 
Crop-Hail Insurance Actuarial Association of 
Chicago, utilizes insurance company records of 
paid hail losses. The purpose of this study is to 
determine whether meteorological parameters 
can be used to define variations in the hail 
hazard in Illinois, and, consequently, be em- 
ployed in establishing hail insurance rates for 
various areas of the State. 
The third study, supported by the Air Force 
Cambridge Research Center (AFCRC), is con- 
cerned with collecting and analyzing radar data 
and volunteer observer reports of hail occur- 
rence to evaluate the utility of radar for identi- 
fying hailstorms. 
This paper presents examples of the data 
used and the types of analysis being performed 
which are of importance in determining the 
physical processes of hail formation. 
Climatological distribution of hailstorms—A 
study was made of the hail distribution in I- 
linois on an annual and seasonal basis. The pur- 
pose of this study was to provide a climatologi- 
369 
cal description of hailstorms in Illinois in respect 
to their average and extreme occurrences. Em- 
phasis was placed on the period from March 
through August, when most hail occurs in the 
State. 
The analysis was based on satisfactory hail 
records between 1901 and 1950 from 85 stations 
in Ilhnois including 12 first-order stations [Huff 
and Changnon, 1959]. Fifty of these 85 stations 
had 20 or more years of reliable hail records. 
Annual hail distribution—The average fre- 
quency of annual hail days is illustrated in 
Figure 1. In this figure, the average has been 
expressed in terms of number of days with hail 
in an average ten-year period. The annual hail 
maximum occurs in the region west of Spring- 
field. Secondary maxima are indicated in ex- 
treme northwest and in southern Illinois. Areas 
of minimum occurrence are indicated in eastern 
Illinois and west of Peoria. 
The areas in northwest and southern Illinois 
do not have elevations exceeding 1200 ft above 
mean sea level. The regions are quite rugged 
locally and the hills rise abruptly from the flat- 
lands to the south in the path of the prevailing 
wind flow. Consequently, it is quite likely that 
the hail maxima in these areas are partially in- 
duced by the abrupt differences in the local 
relief. The area of maximum frequency west of 
Springfield has no pronounced changes in relief 
in relation to the topography of the land sur- 
rounding it. The U. S. Weather Bureau [1947] 
has pointed out that this maximum area, which 
