344 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1960 



At 2000 the first evidence of lightning was noted in a large tower- 

 ing cumulonimbus actively developing in the WNW. By 2040 this 

 stonn was exhibiting continuous lightning. During the next half 

 hour the leading edge had moved into the area, reached, and by 2120 

 had passed, the station. During this period a strong surface wind 

 of 8 to 15 knots flowing from the SE. had been noted. 



At the height of the storm, the pressure jump occurred. This is 

 shown with related data in figure 1. The major change in pressure 

 was preceded by a drop of 6 mb. recorded at 1658. The pressure re- 

 turned to its previous level, fell a few millibars at 2030, then rose 

 rapidly by 12 mb. which it reached at 2145. A pressure jump of 

 8 mb. occurred at the Grand Island airport at 2052. During this 

 period wind gusts reached a peak of 83 knots from 205°, accompanied 

 by hailstones up to 3 inches in diameter. Whether the grapefi'uit 

 sizes mentioned by the newspapers and the "Weather Bureau Clima- 

 tological Report are an exaggeration is not known at present. Such 

 stones have been photographed in the past from tliis general area. 

 Stones of tliis size may have occurred, smce holes were punched 

 through the tail fins of a Flying Tiger cargo plane during the storm. 



A total of 1.09 inches of ram was recorded from the storm with 

 0.65 measured in the 27 minutes between 2129 and 2156. During tliis 

 period, the temperature dropped 15° F. — from 85° F. to 70° F. The 

 maximum for the day was 94° F. readied about 1730. Throughout 

 the day and during the storm, the dewpoint remained almost constant 

 at 69° F. 



The soundings obtained at the nearest radiosonde station, Omaha, 

 Xebr., 115 miles east of Grand Island, indicated a suitable environ- 

 ment over the Great Plains for the development of very large hail- 

 stones. The SELS center in Kansas City forecast stones of 2 inches 

 diameter, using their static analysis method for storms that might 

 form in the Nebraska area in the vicinity of the frontal zone. Accord- 

 ing to information supplied by D. C. House [3], this forecast should 

 have been weighted in favor of stones 3 inches or more in diameter, 

 owing to a definite increase in low-level convergence just prior to the 

 onset of the storm. During this same period, the core of a Jetstream 

 of 60 to 80 loiots velocity swung across the area and probably had a 

 strong influence on the dynamics of the convective clouds above the 

 300 mb. level. 



2. PROPERTIES OF SOxME OF THE HAILSTONES 



Although some reports mentioned hailstones of grapefruit size, the 

 largest ones available for research study were about 2i/2 inches di- 

 ameter. These were shipped to the writer and studied [4] as part of 

 a basic research program [5] in the atmospheric sciences conducted at 



